POLISH JOURNAL OF CHEMISTRY
Volume 72 Number 7S July 1998
A Supplement in Honor of W這dzimierz Ko這s
Pages 1283-1869


CONTENTS

Page

1283 W這dzimierz Ko這s (1928-1996)
— B. Jeziorski and L. Piela
1288 Remembering W這dek Ko這s
— C.C.J. Roothaan
1290 W這dzimierz Ko這s at the Laboratory of Molecular Structure and Spectra,
1957-1968: A Brief Memoir

— B.J. Ransil
1293 Understanding the Adiabatic Approximation; the Accurate Data of H2 Transferred to H3+
— J. Hinze, A. Alijah and L. Wolniewicz
1304 Total Energies and Equilibrium Bond Lengths of Molecules: Myths or Realities, the Example of the Hydrogen Molecule
— J.-M. Andre
1313 The Schroedinger-Riccati Equation. An Application to the Hydrogen and Helium Atoms
— S. Fraga and E.S. Fraga
1323 Non-Adiabatic Couplings between the Final States of Tritium Beta Decay
— S. Jonsell,
A. Saenz and P. Froelich
1334 A General Formula for Shape-Resonance Life Times: The HeH+ Example
— J.M. Peek
1343 Quadrupole Splitting of the Weakly Bound System [(dtµ)11dee]
— D. Bakalov, K. Bakalova,
V. Korobov and H.J. Monkhorst
1353 The Ground State of (He-H-He)+ from Correlated Ab Initio Calculations
— J. Komasa and
J. Rychlewski
1361 A Boundary Condition Determined Wave Function for the H2 (X1 g+ Molecule
— U. Kleinekathoefer, S.H. Patil, K.T. Tang and J.P. Toennies
1376 Polarization Propagator Calculations of Molecular Generalized Oscillator Strengths
— J.R. Sabin and J. Oddershede
1389 Adiabatic Separations of the Vibrational Motions in HeH2+ and the Calculation of the
Metastable States

— V. Spirko, M. Jurek and W.P. Kraemer
1398 Breakdown of the Born-Oppenheimer Approximation in InCl X1+ Electronic State
— M. Molski and J. Konarski
1405 Full CI Calculations of Magnetic Properties of the H2 Molecule in the B1u+ State
— T. Helgaker, M. Jaszunski and K. Ruud
1411 Applicability of the Almost-Linear Coupled-Cluster Method to Nondynamically Correlated States
— I. Grabowski, K. Jankowski and K. Kowalski
1421 Radius of Convergence of the Amos-Musher Intermolecular Perturbation Theory for the
Hydrogen Molecule Ground State

— W.H. Adams
1432 Nonadditive Effects in Small Metal and Polyatomic Molecular Clusters
— O. Novaro
1447 Long-Range Potential for Excess Electron Surface States on Helium Clusters
— J. Jortner and M. Rosenblit
1454 Many-Body Interactions, Symmetry Adapted Perturbation Theory and Chemical Bonding in Beryllium Clusters
— I.G. Kaplan
1464 Dependence of the Solvation Free Energies on Atomic Charge Distribution
— P. Cieplak
1472 Proton Affinities of Rare Gases
— M. Klobukowski
1479 Second Virial Coefficients for Atom-Molecule Complexes from Ab Initio SAPT Potentials
— R. Moszynski, T. Korona, T.G.A. Heijmen, P.E.S. Wormer, A. van der Avoird and B. Schramm
1497 Isoelectronic Dimers [(XH3)2 , (YH2)2 , (ZH)2 , and (Rg)2] in the Groups of the Periodic
System: Ab Initio Quantum Chemical Calculations

— P. Hobza, J.V. Burda and R. Zahradnik
1505 The Influence of the O-H Stretch and O...O Distance on the Many-Body Interactions in the Cyclic Water Trimer
— J. Rak, M.M. Szczesniak, G. Chalasinski and S.M. Cybulski
1524 H-Bridged Gas Phase Clusters of Methanol (Dimers to Hexamers): Ab Initio Calculations of their Structure and Vibrational Spectra
— J. Sauer and A. Bleiber
1540 Periodic Hartree-Fock Studies on (HCl) Chain
— S. Berski and Z. Latajka
1551 Quantum Chemical Description of Catalytic Activation of the C-H Bond
E. Broclawik
1565 Cluster Model Studies on Catalytic Properties of Vanadium Pentoxide
— M. Witko,
R. Tokarz and K. Hermann
1584 Low Frequency Vibrations in Electroabsorption Spectroscopy
— M. Slawik and
P. Petelenz
1593 Carbyne Trefoil Knots - Are they Stable Enough to Exist?
— J.Cz. Dobrowolski and
A.P. Mazurek
1604 Electron Affinity of CH3 and BH3 and the Structure of their Anions
— G.L. Gutsev and
R.J. Bartlett
1615 Ab Initio Theoretical Study of Dipole-Bound Anions of Molecular Complexes. Water Molecule Inhibits or Enhances Electron Affinity of N-Methylaminoadenine
— J. Smets,
D.M.A. Smith, Y. Elkadi and L. Adamowicz
1624 GIAO-CHF and Experimental Study of the Substituent Effects on 13C Magnetic Shielding in Benzene Derivatives
— K. Jackowski, A. Les, A .Dambska and L. Adamowicz
1630 The Existence of Two Isomeric Forms of Monofluorinated Hydrogen Sulfide: A New Theoretical Rationale for Experimentally Observed Infrared Spectrum
— P. Babinec and
J. Leszczynski
1635 Dipole Moment and Polarizability Functions of Ammonia: A Linear-Response Coupled-Cluster Study
— P. Piecuch, V. Spirko and J. Paldus
1657 Prediction of Polymers with Several Optimal Physical Properties
— J.J. Ladik
1667 Ab Initio Protein Folding - Is Conformational Space Searching Enough?
— K.A. Olszewski
1680 Transient Cavities in Liquids and the Nature of the Hydrophobic Effect
— A. Pohorille
1691 On the Hierarchy of -electron Models
— L.Z. Stolarczyk
1737 Variational Calculation of the Global Hardness and the Fukui Function via an Approximation of the Hardness Kernel
— F. De Proft, P. Geerlings, S. Liu and R.G. Parr
1747 Density Functional Method - Principles and Applications
— J. Andzelm
1763 On the Chemical Potential/Electronegativity Equalization in Density Functional Theory
— R.F. Nalewajski
1779 Exploring Bonding Patterns of Molecular Systems Using Quantum Mechanical Bond Multiplicities
— J. Mrozek, R.F. Nalewajski and A. Michalak
1792 Theoretical Density Functional Studies of Tautomeric and Conformational Forms of N4-hydroxycytosine and its 5-fluoro and 5-methyl Derivatives
— G. Bakalarski and B. Lesyng
1798 Electron Localization in Liquid Methanol. Quantum Path-Integral Simulation
— W.M. Bartczak and M. Sopek
1826 Multiple Electron Exchanges in Calculations of Pairwise Nonadditive Contribution to Trimer Interaction Energy
— V.F. Lotrich, K. Szalewicz and B. Jeziorski
1849 Multiple Elliptical-Gaussian-Density Annealing as a Tool for Finding the Most Stable
Structures. Application to Lennard-Jones Atomic Clusters

— J. Pillardy and L. Piela


ABSTRACTS

1288-1289

Remembering W這dek Ko這s

by C.C.J. Roothaan
Hewlett-Packard Laboratories, Palo Alto, California 94304, USA
Professor Emeritus of Physics and Chemistry, University of Chicago, Chicago, Illinois 60637, USA

(Received August 18th, 1997; accepted August 19th, 1997)

1290-1292

W這dzimierz Ko這s at the Laboratory of Molecular Structure and Spectra,
1957-1968: A Brief Memoir

by B.J. Ransil
Departments of Medicine, Beth Israel Hospital and Harvard Medical School, (Ret.),
Department of Neurology, Beth Israel Deaconess Medical Center, Boston, Massachusetts, U.S.A

(Received April 17th, 1997; revised May 30th; 1997, accepted July 15th, 1997)

1293-1303

Understanding the Adiabatic Approximation;
the Accurate Data of H2 Transferred to H3+

by J. Hinze, A. Alijah and L. Wolniewicz
Fakultaet fuer Chemie, Universitaet Bielefeld, 33615 Bielefeld, Germany
Institute of Physics, Nicholas Copernicus University, Torun, Poland

(Received October 6th, 1997; revised October 8th, 1997; accepted October 11th, 1997)

Different ab initio calculations of the rotation-vibrational states of H3+ and its isotopomers are reviewed. In the critical discussion of the results obtained by various authors, we have attempted to analyse the origin of the slight differences remaining (i) due to the inadequacies in the potential surface or (ii) due to the adiabatic approximation used

1304-1312

Total Energies and Equilibrium Bond
Lengths of Molecules: Myths or Realities,
the Example of the Hydrogen Molecule

by J.-M. Andre
Laboratoire de Chimie Theorique Appliquee, Facultes Universitaires Notre-Dame de la Paix
Rue de Bruxelles, 61 B-5000-NAMUR, Belgium

(Received March 27th, 1997; revised December 19th, 1997; accepted December 20th, 1997)

In this paper, simple considerations of use in everyday quantum chemistry are reviewed. They stress the fact that the "classical" concepts of total energy and of bond lengths in molecules are based on severe approximations and are not as such accessible to direct experimentation, due to Heisenberg's uncertainty principle and to its main consequence in molecules: the existence of a residual zero point vibration. In this paper, we address successively (a) the determination of total energies, and (b) the meaning of an "equilibrium" bond length.

1313-1322

The Schroedinger-Riccati Equation. An Application
to the Hydrogen and Helium Atoms

by S. Fraga and E.S. Fraga
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
Department of Chemical and Biochemical Engineering, University College London,
Torrington Place, London WC1E 7JE, U.K.

(Received March 25th, 1997; revised May 25th, accepted June 1st, 1997)

Numerical results for the ground states of the hydrogen and helium atoms confirm the validity of the algebraic Schroedinger-Riccati equation. A quartic equation may be appropriate for points in the electron configuration space corresponding to electron positions close to the nucleus but a higher degree will be needed for the outer regions. The Schroedinger-Riccati equation is appropriate for implementation in parallel-computing facilities and its practical applicability will be enhanced by the availability of high-speed computers.

1323-1333

Non-Adiabatic Couplings between the Final States
of Tritium Beta Decay

by S. Jonsell1, A. Saenz1,2 and P. Froelich1
1Department of Quantum Chemistry, Uppsala University, Box 518, S-75120 Uppsala, Sweden
2Fakultaet fuer Chemie, Universitaet Konstanz, Postfach 5560 M722, D-78434 Konstanz, Germany

(Received April 3rd, 1997; revised June 26th, 1997; accepted June 30th, 1997)

The non-adiabatic couplings between the ground state and the first 5 excited states in 3HeT+ have been calculated. Non-adiabatic corrections to the ß-decay spectrum of T2 are derived in first-order perturbation theory. These corrections are estimated to be less than 0.01%.

1334-1342

General Formula for Shape-Resonance Life Times:
The HeH+ Example

by J.M. Peek
45 Puye, Los Alamos, New Mexico 87544, U.S.A.

(Received April 8th, 1997; revised June 4th, 1997; accepted June 15th, 1997)

Translational spectroscopy stimulated the investigation of shape resonances in the electronic ground state of HeH+ a number of years ago. Subsequent spectroscopic studies have increased the accuracy of these experimental data. Theoretical investigations require an extremely accurate potential energy curve over an extended range of internuclear separation. The calculation by Ko這s proved invaluable in identifying these states and continues to be the standard to which improvements are added. The accurate characterization of many isolated shape resonances may be necessary so convenient techniques are required. Test functions are often used to create a boundary condition that converts this problem in the continuum to a discrete state calculation. The resulting eigenvalue search is efficient and convenient to automate. The associated widths are usually found by other techniques. It is shown here that the eigenvalue calculation implies a width if one convenient and easily satisfied requirement is met. Two versions of this result are applied to selected experimental data for HeH+.

1343-1352

Quadrupole Splitting of the Weakly Bound System [(dtµ) 11dee]

by D. Bakalov1, K. Bakalova2, V. Korobov3 and H.J. Monkhorst4
1Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria
2Solar-Terrestrial Influences Laboratory, Sofia, Bulgaria
3JINR, Dubna, Russia
4QTP, University of Florida, Gainesville, FL32611

(Received April 30th, 1997; revised May 19th, 1997; accepted May 30th, 1997)

The energy levels of the molecular complex [(dtµ)11dee] are close to the sum of the energies of the (dtµ)11 and D2 molecules; the small difference of a few meV, referred to as "finite size correction", is an effect of the Coulomb interaction with the spatially distributed electrical charge in the compound nucleus of the complex. The quadrupole terms in the multipole expansion of the latter are shown to interfere with the spin interactions and to modify the hyperfine structure of the levels of the complex in a way that may affect the resonant formation rate of (dtµ)11.

1353-1360

The Ground State of (He-H-He)+ from
Correlated Ab Initio Calculations

by J. Komasa1 and J. Rychlewski2
1Department of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
2Department of Chemistry, A. Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland and
Poznan Supercomputing and Networking Center, Wieniawskiego 17/19, 61-713 Poznan, Poland

(Received April 27th, 1997; accepted June 30th, 1997)

He2H+ ion in its ground state is studied by means of ab initio methods taking into account the electron correlation. Geometry optimization at the CCSD(T)/cc-pV5Z level of theory has been performed and the potential energy hypersurface scan is presented. The optimum conformation is linear and symmetric with the proton at the He-He midpoint and the He-H distance equal to 1.75 bohr. Stabilization energy with respect to the He2H+ HeH+ + He dissociation channel has been computed. Additionally, a single point variational calculations with the use of the Exponentially Correlated Gaussian wave functions have been performed. They supply an upper bound to both the total electronic energy (-5.903505 hartree) and the stabilization energy (-13.224 kcal/mol). A comparison of the results from both the perturbational coupled cluster and variational methods is presented.

1361-1375

A Boundary Condition Determined Wave Function
for the H2 (X1g) Molecule

by U. Kleinekathoefer1,2, S.H. Patil1,3, K.T. Tang1,4 and J.P. Toennies1
1Max-Planck-Institut fuer Stroemungsforschung, Bunsenstr.10, D-37073 Goettingen, Germany
2Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
3Department of Physics, Indian Institute of Technology, Bombay 400076, India
4Institute of Atomic and Molecular Sciences, Academica Sinica,
P.O.Box 23-166, Taipei, Taiwan 106, Republic of China

(Received April 9th, 1997; revised May 24th, 1997; accepted June 3rd, 1997)

Two relatively simple non-variational wave functions for two electron diatomic molecules are proposed. The electron-electron cusp condition is satisfied rigorously by a correlation function which has the correct behavior for r12 0 and r12 . The electron-nucleus cusp conditions are also rigorously satisfied by the proposed functional forms of the wave functions. The parameters are chosen to match the asymptotic conditions in two different approximations. Both wave functions yield very good energies for the chemical bond. This demonstrates that these local conditions have a big effect on the wave function.

1376-1388

Polarization Propagator Calculations of Molecular Generalized Oscillator Strengths

by J.R. Sabin and J. Oddershede
Kemisk Institut, Odense Universitet, 5230 Odense M, Denmark Quantum Theory Project,
Department of Physics, University of Florida, Gainesville, FL 32611 U.S.A.

(Received May 21th, 1997; revised July 5th, 1997; accepted July 15th, 1997)

The linear energy deposition, or stopping power, of materials for swift ions is determined, at the level of the first Born approximation, by the generalized oscillator strength distribution of the target. Here we consider the calculation of generalized oscillator strengths for several low lying transitions in small molecules using the polarization propagator approach, with emphasis on their directional characteristics.

1389-1397

Adiabatic Separations of the Vibrational Motions
in HeH2+ and the Calculation of Metastable States

by V. Spirko1, M. Jurek1 and W.P. Kraemer2
1J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejskova 3, CZ-18223 Praha 8, Czech Republic
2Max-Planck-Institute of Astrophysics, Postfach 1523, D-85740 Garching, Germany

(Received June 8th, 1997; accepted July 5th, 1997)

Recent ab initio calculated potential energy data for the ground electronic state of HeH2+ are used to construct a new potential function, which is suitable to describe the interaction between He and H2+ at low collision energies. All bound and the lowest quasi-bound rotation-vibrational levels of HeH2+ are evaluated within the framework of the Sutcliffe-Tennyson Hamiltonian for triatomic molecules neglecting Coriolis interactions between the states. Adiabatic separations of the vibrational motions are used to simplify the calculation of the bound and quasi-bound levels close to the dissociation limit. Comparison with the results of full-dimensional calculations shows that a very good agreement is obtained when separating adiabatically the high-frequency H2+ stretching motion from the remaining two low-frequency modes and that further separation of the low-frequency motions still provides useful approximations for the positions of the bound and lowest quasi-bound states.

1398-1404

Breakdown of the Born-Oppenheimer Approximation in InCl X1+ Electronic State

by M. Molski and J. Konarski
Department of Theoretical Chemistry, Faculty of Chemistry, Adam Mickiewicz University,
ul. Grunwaldzka 6, 60-780 Poznan, Poland

(Received April 9th; revised June 6th, 1997; accepted June 15th, 1997)

Pure rotational transitions of 115In35Cl, 115In37Cl, 113In35Cl and 113In37Cl were analyzed to yield mass-independent radial parameters representing the internuclear potential energy and nonadiabatic rotational effects of the nuclei. From the determined t0In,Cl parameters, reflecting the purely the nonadiabatic rotational effects, and from experimental value of the dipole moment the rotational g-factor of four isotopic variants of InCl has been evaluated. The quality of the Born-Oppenheimer approximation and the extent of its breakdown in indium monochloride have been examined.

1405-1410

Full CI Calculations of Magnetic Properties
of the H2 Molecule in the B1u+ State

by T. Helgaker1, M. Jaszunski1,2 and K. Ruud1
1Department of Chemistry, University of Oslo, Box 1033, Blindern, N-0315 Oslo, Norway
2Institute of Organic Chemistry, Polish Academy of Sciences, 01 224 Warszawa, Kasprzaka 44, Poland

(Received February 2nd, 1997; revised March 11th, 1997; accepted March 11th, 1997)

The magnetizability, the g-factor, the NMR shielding constant and the spin-rotation constant of the hydrogen molecule in the B1u+ state are studied in the full Configuration Interaction (full CI, FCI) approach. A GIAO orbital basis is used to ensure gauge-origin indepedence of the computed properties. Their dependence on basis set and internuclear distance is analysed. Our results for the magnetizability confirm that this excited state of H2 is paramagnetic. The paramagnetism of this state is also reflected by the values of the other properties.

1411-1420

Applicability of the Almost-Linear Coupled-Cluster Method to Nondynamically Correlated States

by I. Grabowski, K. Jankowski and K. Kowalski
Institute of Physics, Nicholas Copernicus University, 87-100 Torun, Poland

(Received April 14th, 1997; accepted July 8th, 1997)

To study the reliability of the almost-linear coupled-cluster (AL-CC) approach when applied to the description of states disclosing nondynamical correlation (or quasidegeneracy) effects, calculations have been performed for several systems widely used in quantum-chemical model calculations for quasidegenerate states (H4 (MBS), H2O (DZ), BeH2 (DZ), BH (DZP)).
The AL-CC approach represents a special application of the recently formulated split-amplitude strategy for approximating the equations of the CC methods (Chem.Phys. Lett., 256,141(1996)) which consist in splitting the individual cluster amplitudes into two components - one of fixed value and the other determined from a set of modified CC equations. The linearization of the latter set yields the equations of the AL-CC method. In the present study the cluster operator is represented in terms of one- and two-body operators (AL-CCSD). The energies calculated are free from the singular behavior of their counterparts obtained for some strongly quasidegenerate states when using the standard linearized CC methods (L-CCSD). Outside the very strong quasidegeneracy region the AL-CCSD energies are very close to the CCSD ones, which demonstrates the usefulness of the low cost AL-CC approach.

1421-1431

Radius of Convergence of the Amos-Musher
Intermolecular Perturbation Theory
for the Hydrogen Molecule Ground State

by W.H. Adams
Wright and Rieman Chemistry Laboratories Rutgers University New Brunswick, NJ 08903 U.S.A.
Email: adams@rutchem.rutgers.edu

(Received April 17th, 1997; revised June 18th, 1997; accepted June 19th, 1997)

We have approximately determined the radius of convergence of the Amos-Musher perturbation theory applied to the hydrogen molecule at nuclear separations ranging from 3 to 12 bohr. We have done this by approximately locating for the lowest eigenvalue of the Amos-Musher Hamiltonian those branch points which are closest to the center about which the perturbation expansion is developed. Using the same method and basis set we have also located the branch points of the Polarization Approximation applied to H2 and obtained results in good agreement with the accurate values found a few years ago by Cwiok, Jeziorski, Ko這s, et al. We find that the radius of convergence of the Amos-Musher theory increases from 1.7 times as large as that of the Polarization Approximation at 3 bohr to twice as large at 8 to 12 bohr. This shows that the Amos Musher theory differs fundamentally from the Polarization Approximation.

1432-1446

Nonadditive Effects in Small Metal
and Polyatomic Molecular Clusters

by O. Novaro
Instituto de Fisica, UNAM Apdo. Postal 20-364, Mexico 01000, D.F., Mexico

(Received February 19th, 1997, revised January 5th, 1998; accepted January 10th, 1998)

A review of the role of multibody effects in the behavior of oligomer bound states, crystalline structures, adsorption properties of surfaces and dense states of matter is given. Special emphasis is placed on the work of W. Ko這s and coworkers in the Universities of Warsaw and Mexico. New results including electron correlation are given here, confirming the enormous role played by the multibody corrections in the stability of metallic clusters as Lin and Ben, where nonadditive effects are very large, to the point of making the convergence of the multibody expansion of the energy extremely doubtful. For polyatomic molecular clusters as (NH3)3 multibody effects albeit small, still are quite relevant to determine the cluster stability and geometry.

1447-1453

Long-Range Potential for Excess Electron
Surface States on Helium Clusters

by J. Jortner and M. Rosenblit
School of Chemistry, Tel-Aviv University, Tel Aviv 69978, Israel

(Received October 2nd, 1997; accepted October 10th, 1997)

An excess electron bound to a (4He)N cluster (number of constituents N 3 x 105 and cluster radius R Rc = 149 ) exhibits a divergence of the first moment of the charge distribution near the localization threshold (R = Rc), obeying the scaling law <r> (R - Rc)-1. The asymptotic form of the electron-cluster potential has to be modified to include Casimir-Spruch retardation effects, which provide a small repulsive contribution O(/mc)r-1.

1454-1463

Many-Body Interactions, Symmetry Adapted
Perturbation Theory and Chemical Bonding
in Beryllium Clusters

by I. G. Kaplan
Instituto de Fisica UNAM, Apdo. Postal 20-364, 01000 Mexico, D. F. MEXICO

(Received May 13th, 1997; revised June 15, 1997; accepted June 19, 1997)

The general formulae for the decomposition of many-body interaction energies in the double SAPT and the ab initio model potential for the Be3 cluster are presented. The analysis of exchange and dispersion contributions to the model potential allows to elucidate the nature of binding in beryllium clusters. Two kind of stabilizing forces are responsible for binding: the additive local van der Waals forces and the nonadditive delocalized exchange forces.

1464-1471

Dependence of the Solvation Free Energies
on Atomic Charge Distribution

by P. Cieplak
Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

(Received April 14th, 1997; revised April 30th, 1997; accepted June 3th, 1997)

The dependency of hydration free energies on the atomic charge distribution has been studied using the free energy perturbation method and molecular dynamics simulations. Several hypothetical sets of atomic charges for methanol molecule have been constructed, yielding the same total molecular dipole moment of 2.14 D. Each of the sets has been perturbed into another one and the electrostatic contributions to the hydration free energy differences associated with such changes have been determined. The magnitude of calculated electrostatic contribution to the solvation free energies crucially depends on the position of the center of charge and orientation of the total dipole moment within molecular van der Waals envelope. It depends less on higher molecular multipole moments. The issue of convergence of the electrostatic contribution to the free energies obtained from molecular dynamics simulations will be also addressed.

1472-1478

Proton Affinities of Rare Gases

by M. Klobukowski
Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2 Canada

(Received April 28th, 1997; accepted May 9th, 1997)

Density functional theory and large Gaussian basis sets were employed in the studies of the molecular ions HeH+, NeH+, and ArH+. The calculated proton affinities of 42, 49-51, and 90-92 kcal/mol for the three rare gases He, Ne, and Ar agree reasonably well with the experimental values of 42, 49, and 88 kcal/mol. Spectroscopic constants for the ions were evaluated and compared with other accurate values.

1479-1496

Second Virial Coefficients for Atom-Molecule
Complexes from Ab Initio SAPT Potentials

by R. Moszynski1, T. Korona1, T.G.A. Heijmen2, P.E.S. Wormer2,
A. van der Avoird2, and B. Schramm3
1Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
2Institute of Theoretical Chemistry, NSR Center, University of Nijmegen,
Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
3Physikalisch-Chemisches Institut, Ruprecht-Karls-Universitaet Heidelberg,
Im Neuenheimer Feld 500, D-69120 Heidelberg 1, Germany

(Received May 6th, 1997; revised June 15th, 1997; accepted June 17th, 1997)

Ab initio potentials, calculated by symmetry-adapted perturbation theory, are applied to compute second virial coefficients (including first order quantum corrections) for He-CO, Ne-CO, Ar-H2, He-C2H2, and Ar-CH4 mixtures over a wide range of temperatures. The experimental methods are briefly outlined and the errors in the procedure to obtain mixed virial coefficients from the experimental data are discussed. Very good agreement with the majority of the available experimental data is observed for all systems except Ar-CH4 where calculated virial coefficients are slightly too high in comparison with measured data. Possible reasons for discrepancies between theory and experiment at very low temperatures are discussed.

1497-1504

Isoelectronic Dimers [(XH3)2, (YH2)2, (ZH)2, and (Rg)2] in the Groups of the Periodic System:
Ab initio Quantum Chemical Calculations

by P. Hobza, J.V. Burda and R. Zahradnik
J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejskova 3, 182 23 Prague 8, Czech Republic

(Received April 17th, 1997; accepted May 7th, 1997)

The (ZH)2, (YH2)2, (XH3)2 and (Rg)2 dimers [Z = F-At; Y = O, Po; X = N, Bi; Rg = rare gas] were studied ab initio using the CCSD(T) and MP2 procedures. Average relativistic effective potentials were used for all the halogens, while Stuttgart effective core potentials were used for the remaining non-hydrogen atoms. All the (HX)2 structures are H-bonded. All the stabilization energies mutually approach when passing down the group of the periodic system.

1505-1523

The Influence of the O-H Stretch and O...O
Distance on the Many-Body Interactions in the
Cyclic Water Trimer

by J. Raka,b, M.M. Szczesniaka, G. Chalasinskic and S.M. Cybulskid
aDepartment of Chemistry, Oakland University, Rochester, Michigan 48309, USA
bDepartment of Chemistry, University of Gdansk, 80-952 Gdansk, Poland
cDepartment of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
dDepartment of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, USA

(Received June 4th, 1997; accepted June 17th, 1997)

The effects of the O-H stretch and changes in the O...O distance upon the one-, two- and three-body interaction energy components were studied in a cyclic water trimer. Calculations were carried out using supermolecular Moeller-Plesset perturbation (S-MPPT) theory in conjunction with perturbation theory of intermolecular forces, also known as intermolecular Moeller-Plesset theory (I-MPPT). The dependence of the one-body relaxation as well as electrostatic, induction, exchange and dispersion terms upon changes in the intramolecular O-H bond length and upon the intermolecular O...O distance were studied to identify the term which have the strongest influence on the structural parameters of the trimer. We found that the one-body terms must be evaluated at a high level of theory (MP4) with an elaborate basis set. The two-body perturbation energies appear to be reliably reproduced through the second order (MP2), and the three-body terms are reliable already at the self consistent field (SCF) level of theory. The two-body and three-body terms vary approximately linearly with the OH stretch of proton-donors.

1524-1539

H-bridged Gas Phase Clusters of Methanol
(Dimers to Hexamers): Ab Initio Calculations
of their Structure and Vibrational Spectra

by J. Sauer and A. Bleiber
Max Planck Gesellschaft, Arbeitsgruppe "Quantenchemie" an der Humboldt-Universitaet Berlin, Jaegerstrasse 10/11, D-10117 Berlin, Germany

(Received September 25th, 1997; revised November 27th, 1997; accepted November 30th, 1997)

Hartree-Fock calculations using a polarized basis set are performed on methanol clusters of two to six molecules. Electron correlation is included by second order Moeller-Plesset perturbation theory for the trimer and the structure of the hexamer only. Starting from trimers, among several optimized structures the cyclic ones are found most stable. Harmonic vibrational frequencies and infrared intensities are calculated and comparison is made with observed spectra in the CO ad OH stretch region.

1540-1550

Periodic Hartree-Fock Studies on (HCl) Chain

by S. Berski and Z. Latajka
Faculty of Chemistry, University of Wroclaw, 14 F. Joliot-Curie, 50-383 Wroclaw, Poland

(Received May 19, 1997; accepted June 10th, 1997)

The infinite chain of hydrogen chloride (HCl) is studied by the periodic Hartree-Fock (PHF) method using CRYSTAL 92 program. The basis sets of double zeta type containing sp- diffuse as d- and p- polarisation functions are investigated. The relationship between structural and energetic parameters of (HCl)C and these basis sets is discussed. Furthermore, it is shown that [12s9p/6s4p] basis set of Veillard and Huzinaga, which was successfully used in studies on HCl dimer, yields the best geometry of the infinite chain. Based on this basis set, the height of the barrier for proton transfer is obtained with value of 39.6 kcal/mol. The comparison of the density of states plots (DOS) computed for (HF) and (HCl) indicates that computational level influences rather slightly the DOS function in case of the hydrogen chloride chain.

1551-1564

Quantum Chemical Description
of Catalytic Activation of the C-H Bond

by E. Broclawik
Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Cracow, Poland

(Received April 9th, 1997; revised June 30th, 1997; accepted July 1st, 1997)

Density functional theory is presented from the point of view of its applicability in modelling catalytic reactions. Reaction paths for C-H bond scission in methane interacting with metal oxide/transition metal catalytic sites for gallium oxide in zeolitic lattice and palladium or rhodium based supported catalysts are analysed. On the basis of interdependence between the electronic structure and reactivity of the bond two mechanisms for the activation of the C-H bond are described: via electrons withdrawal from bonding states (on oxide catalysts) and via electron insertion to antibonding orbitals (on metals).

1565-1583

Cluster Model Studies on Catalytic Properties
of Vanadium Pentoxide

by M. Witko1, R. Tokarz1 and K. Hermann2
1Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences,
ul. Niezapominajek, 30 239 Cracow, Poland
2Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

(Received April 8th, 1997, accepted May 10th, 1997)

ZINDO cluster model calculations are performed to study the electronic structure and chemical reactivity of the V2O5(010) surface. Inter-atomic binding in vanadium pentoxide is determined to be of a mixed ionic and covalent character. The calculations reveal the difference in the catalytic properties between structurally inequivalent surface oxygen centers and show the increased local reactivity of bridging oxygens with respect to the electrophilic adparticles. Convergence of the electronic properties with respect to the cluster size is achieved for cluster as large as V10O31H12. The effect of the second substrate layer on the surface electronic properties is found to be negligible. Further, rather similar electronic parameters of the V10O31H12 cluster in its idealized, bulk and optimized geometry are obtained. The H/H+ species adsorb at the V2O5(010) surface, always at oxygen sites, forming very stable surface hydroxyl groups. The strongest binding occurs with the oxygen O(c) bridging two bare vanadium atoms. These O(c) oxygens become quite mobile in presence of the H/H+ adparticle. Allowing the surface oxygens to relax during adsorption of H/H+ leads to different adsorption scenarios depending on the surface oxygen site. At the vanadyl oxygen site a very stable and rigid hydroxyl group O(a)H is formed above the vanadium center. At the doubly coordinated oxygen site O(b) the adsorbate penetrates between two vanadyl groups to form a local O(b)H group, while at the O(c) site an O(c)H group is created (slightly above the surface O(c) position), where O-H binding is strongest. Weak initial interaction, between triply coordinated oxygens O(d,e) and the incoming H/H+ species, leads to stabilization of the adsorbate near the closest vanadyl site resulting in a tilted O(a)H group instead of O(d)H or O(e)H.

1584-1592

Low Frequency Vibrations
in Electroabsorption Spectroscopy

by M. Slawik and P. Petelenz
Department of Theoretical Chemistry, Jagiellonian University, 30-060 Krakow, Ingardena 3, Poland

(Received April 9th, 1997; accepted May 30th, 1997)

A simple two-state, two-mode model is proposed to probe the role of low-frequency vibrations in electroabsorption (EA) spectroscopy. The results demonstrate that explicit inclusion of such vibrations in the model is necessary to reproduce the EA signals of Frenkel states, but essentially irrelevant for CT states.

1593-1603

Carbyne Trefoil Knots - Are They Stable
Enough to Exist?

by J.Cz. Dobrowolski1,2 and A.P. Mazurek2
1Industrial Chemistry Research Institute, 8 Rydygiera Street, 01-793 Warsaw, Poland
2Drug Institute,30-34 Chelmska Street, 00-725 Warsaw, Poland

(Received March 27th, 1997; revised June 6th, 1997; accepted June 15th, 1997)

The structure and stability of non-linear carbon clusters of carbyne type was estimated based on ab initio quantum mechanical calculations. Both the cyclic (cycarbynes) and knotted (knocarbynes) trefoil structures of closed polycarbon chains, containing up to 84 carbon atoms, were considered. Comparison of the calculated spectral properties (IR, 13C NMR) with those of C60 fullerene provide the basis for experimental identification of Cn cyclic and knotted structures as may have implication for interstellar dust spectroscopy.

1604-1614

Electron Affinity of CH3 and BH3
and the Structure of their Anions

by G.L. Gutsev and R.J. Bartlett
Quantum Theory Project, P.O. Box 118435, University of Florida, Gainesville, FL 32611-8435

(Received April 29th, 1997; revised June 3th, 1997, accepted June 30th, 1997)

The electronic and geometrical structure of the methyl radical, CH3, the borane molecule, BH3, as well as their anions CH3- and BH3- are calculated with the Hartree-Fock Density Functional Theory (HFDFT), fourth-order many-body perturbation theory (MBPT(4)), and the coupled-cluster (CCSD(T)) methods with the use of the large atomic natural orbital basis of Widmark-Malmqvist-Roos. Potential energy surfaces of BH3 and BH3- symmetric stretchings and out-of-plane C3nu hydrogen motions of CH3 and CH3- are obtained at the MBPT(4)/6-311++G(3df, 3pd) level. At the CCSD(T) level of theory, the difference in the total electronic energies of CH3 and CH3- is 0.01 eV and that of BH3 and BH3- is -0.05 eV. Corrected for the zero-point energies (ZPE) of nuclear motions, the adiabatic electron affinities (EAad) of CH3 and BH3 are 0.05 and 0.01 eV, respectively, being in nice agreement with the experimental values of 0.08±0.03 and 0.038±0.015, respectively. Thus, the EAads of CH3 and BH3 are defined mainly by the differences in the ZPEs of the corresponding neutral-anion pairs.

1615-1623

Ab-Initio Theoretical Study of Dipole-Bound Anions of Molecular Complexes. Water Molecule Inhibits or
Enhances Electron Affinity of N-Methylaminoadenine

by J. Smets, D.M.A. Smith, Y. Elkadi and L. Adamowicz
Department of Chemistry, University of Arizona, Tucson, Arizona 85721, U.S.A.

(Received April 28th, 1997, accepted May 30th, 1997)

Ab initio calculations have been performed to determine the electron affinity of the water complex of N-methylaminoadenine (NMA). This complex has been chosen for this study because it can form three different isomeric structures with a water molecule hydrogen-bonded at three different NMA sites, and only two of these structures have sufficient dipole moments to form dipole-bound states with an excess electron. In the third structure, which according to the calculations should be the most stable form, the dipole moments of NMA and the water molecule oppose each other resulting in an almost null dipole moment of the complex, so the complex has no ability to form a stable dipole-bound anion. This determination offers an interesting possibility for an experimental investigation of whether the NMA.H2O complex forms an stable anion. If such an anion is detected, it will mean that an electron attachment can increase the gas- phase concentration of the complex, which is thermodynamically less stable in its neutral form.

1624-1629

GIAO-CHF and Experimental Study of the Substituent Effects on 13C Magnetic Shielding in Benzene Derivatives

by K. Jackowski1, A. Les1, A. Dambska1 and L. Adamowicz2
1Department of Chemistry, The University of Warsaw ul. Pasteura 1, 02-093 Warszawa, Poland
2Department of Theoretical Chemistry, The University of Lund, Chemical Center,
P.O.B. 124, S-22100 Lund, Sweden

(Received March 15th, 1997; revised May 5th, 1997; accepted May 6, 1997)

Ab initio calculations of the 13C shielding constants were performed with the use of the GIAO-CHF method for the benzene molecule and its 14 monosubstituted derivatives. The theoretical substituent effects were compared with our experimental data which were measured in cyclohexane solutions and extrapolated to infinite dilution. Satisfactory correlations between theoretical and experimental results were observed for all the aromatic carbons except those in the meta position.

1630-1634

The Existence of Two Isomeric Forms
of Monofluorinated Hydrogen Sulfide:
A New Theoretical Rationale for Experimentally
Observed Infrared Spectrum

by P. Babinec1,2 and J. Leszczynski1
1Department of Chemistry, Jackson State University, P.O. Box 17910, Jackson, MS 39217, USA
2Department of Chemical Physics, Comenius University, Bratislava, Slovakia

(Received March 13th, 1997; accepted April 4th, 1997)

In order to explain the discrepancies between the matrix isolated IR spectra of the products of the H2S + F2 reaction and recent computational studies of this system, we have analyzed the potential energy surface of monofluorinated hydrogen sulfide using high level post-Hartree-Fock methods. The molecular geometries and harmonic vibrational frequencies were calculated at the DFT, MP2, and CCSD levels in conjunction with the 6-311++G(d,p) basis set. Besides the already proposed HSF isomer which corresponds to the global energetic minimum, a local minimum corresponding to the HFS isomer as well as a transition state structure between these minima have been also characterized. The calculated vibrational frequencies fit well with the experimental IR spectra and also complement previous ab initio calculations on the HSF isomer.

1635-1656

Dipole Moment and Polarizability
Functions of Ammonia:
A Linear-Response Coupled-Cluster Study

by P. Piecuch1, V. Spirko2 and J. Paldus3
1Department of Chemistry, University of Toronto, 80 St. George Street,
Toronto, Ontario, Canada M5S 3H6
2J. Heyrovsk<203> Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,
Dolejskova 3, 18223 Prague 8, Czech Republic
3Quantum Theory Group, Department of Applied Mathematics,
and Department of Chemistry and (GWC)2 - Waterloo Campus, University of Waterloo,
Waterloo, Ontario, Canada N2L 3G1

(Received August 20th, 1997; revised September 25th, 1997; accepted October 1th, 1997)

The recently developed orthogonally spin-adapted linear-response coupled-cluster theory with singly and doubly excited clusters (LRCCSD) has been employed to calculate the dipole moment and parallel polarizability functions of ammonia over a wide range of values of the inversional and symmetric stretch coordinates. Using the eigenstates of the experimentally derived nonrigid invertor Hamiltonian of ammonia and the LRCCSD property functions, the transition dipole moments between several low-lying inversional states and the rovibrationally averaged parallel polarizabilities for several values of the inversional quantum number have been evaluated. The calculated transition dipole moments and rovibrationally averaged polarizabilities have been found to be in excellent agreement with the available experimental and theoretical data, indicating the suitability of the ab initio LRCCSD theory for such calculations. The LRCCSD transition dipole moments are far more accurate than all previously obtained ab initio values.

1657-1666

Prediction of Polymers with
Several Optimal Physical Properties

by J.J. Ladik
Chair for Theoretical Chemistry and Laboratory of the National Foundation of Cancer Research of the Friedrich-Alexander University Erlangen-Nuremberg, Egerlandstr. 3, D-91058 Erlangen, Germany

(Received June 4th, 1997; accepted July 4th, 1997)

First a brief review is given of the ab initio Hartree-Fock and correlation corrected band structure calculation methods of periodic 1D and 2D polymers. In the 1D case, the extension of the theory to disordered chains leading to the calculation of variable range hopping conductivity of some native proteins is also outlined. In the cases of the ground state properties of (SN)x, for the vibrational and excitonic spectra of organic - and biopolymers good agreement could be obtained with experiment. The same has been achieved for the fundamental gap of different organic polymers, for the bulk modulus of polyethylene and for the hopping conductivity along their main chains of insulin and lysozyme. These examples demonstrate that if one applies sophisticated enough theoretical metohods, any kind of physical property of any kind of periodic or non-periodic quasi-1D polymer can be computed in good agreement with experiment.
This opens up the possibility to predict polymers with optimal 3- 5 non-related properties from a family of polymers with a huge number of members. The prediction of such "tailor-made" polymers is of course of large practical importance. It is discussed that such a theoretical approach to find polymers with 4-5 optimal properties is much less expensive (and it will be still less expensive in the future) than the classical procedure to synthetize and measure the properties of a larger number of polymers.

1667-1679

Ab initio Protein Folding - Is Conformational Space Searching Enough?

by K.A. Olszewski
Molecular Simulations Inc., 9685 Scranton Rd., San Diego, CA 92121, USA

(Received May 21th, 1997; accepted May 30th, 1997)

Ab initio protein folding is a common name for protein structure prediction approaches, that explore the conformational space of a protein using a model of a protein and a simple, carefully designed, potential energy function. Attempts to predict the native state of the protein or to reproduce the folding pathway from a set of simple rules are essential for an understanding of the physico-chemical rules that govern the folding process. Noteworthy, a number of new techniques for protein structure/function prediction that widen the search space and the meaning of the potential energy function have emerged. In this paper the variety of approaches to protein structure or function prediction are discussed and classified with respect to their distribution in the general protein sequence-structure space.

1680-1690

Transient Cavities in Liquids and the Nature
of the Hydrophobic Effect

by A. Pohorille1,2
1Exobiology Branch, NASA - Ames Research Center MS 239-4 Moffett Field, California 94035-1000
2Department of Pharmaceutical Chemistry, University of California,
San Francisco, California 94143

(Received June 15th, 1997; revised July 30th, 1997; accepted August 15th, 1997)

The size distributions of transient cavities in water and organic liquids, obtained from computer simulations, have provided a new means to analyze the nature of the hydrophobic effect and to evaluate the adequacy of different analytical models of this effect. The poor solubility of non-polar solutes in water is attributed to a low probability of finding in water cavities of atomic and molecular size. It has been shown that water applies more force per unit area of cavity surface than do hydrocarbon liquids. Models that successfully capture the main characteristics of the hydrophobic effect must at least include information about the density and the radial distribution of oxygen atoms in liquid water. One such model, quantitatively accurate for molecular solutes of arbitrary shape, is presented.

1691-1736

On the Hierarchy of -electron Models

by L.Z. Stolarczyk
Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

(Received November 17th, 1997; accepted November 26th, 1997)

A systematic derivation of -electron models is given, based on a spin-restricted formulation of the molecular-orbital (MO) model for closed- and high-spin open-shell states. A chain of step-by-step approximations leads to the following top-down hierarchy of MO models: ab initio (- separation) Pariser-Parr-Pople (PPP) Hubbard ,ß-selfconsistent Hueckel Molecular Orbital (HMO) ß-selfconsistent HMO "basic" HMO. The PPP semiempirical parameters ('s, ß's, and 's) are related to exact MO formulas, and the limitations of the PPP MO model are discussed. In general, the parameters of a given -electron model are related to those of the preceding one, and limitations of the introduced approximations are indicated. It is shown, for instance, that for the closed-shell alternant hydrocarbons the ß-selfconsistent HMO model, applied for describing the properties of molecular ground-state (equilibrium geometry, thermochemical stability), is equivalent to the more advanced Hubbard model.

1737-1746

Variational Calculation of the Global Hardness
and the Fukui Function via an Approximation
of the Hardness Kernel

by F. De Proft1, P. Geerlings1, S. Liu2 and R. G. Parr2
1Enheid Algemene Chemie, Vrije Universiteit Brussel, Falculteit Wetenschappen,
Pleinlaan 2, 1050 Brussels, Belgium
2Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, USA

(Received May 20th, 1997; accepted July 4th, 1997)

An implementation of the variational principle for the chemical hardness [P.K. Chattaraj, A. Cedillo and R.G. Parr, J. Chem. Phys., 103, 7645(1995)] is described, which uses a simple approximation to the hardness kernel. The molecular Fukui function is taken to be a linear combination of atomic Fukui functions, which are expanded in a set of Gaussian type orbitals. This methodology is shown to yield results which are largely in agreement with sensitivity analysis methods of Mortier, Nalewajski, and coworkers.

1747-1762

Density Functional Method - Principles
and Applications

by J. Andzelm
Molecular Simulations, Inc., 9685 Scranton Rd, San Diego, CA 92121

(Received May 30th, 1997, accepted July 4th, 1997)

An overview of the main concepts of Density Functional Theory from a historical perspective is given. Most popular techniques of solving DFT equations currently used in chemistry are listed. Applications of the DFT method to study chemical reactions using various levels of DFT theory are discussed. Local DFT is successful in predicting molecular structures with covalent bonds. However, in general it should not be used to study energetics of reactions and systems with weak interactions. The next level of theory, nonlocal DFT, is a preferable choice for the study of thermochemistry. Investigation of reaction barriers may require a higher level of theory, so called hybrid methods that use a portion of the exact Hartree-Fock exchange.

1763-1778

On the Chemical Potential/Electronegativity
Equalization in Density Functional Theory

by R.F. Nalewajski
K. Guminski Department of Theoretical Chemistry, Jagiellonian University,
R. Ingardena 3, 30-060 Cracow, Poland

(Received March 7th, 1997; accepted March 20th, 1997)

General variational principles of the Kohn-Sham (KS) density functional theory are interpreted as the corresponding chemical potential/electronegativity equalization equations. The unconstrained (ground-state) and constrained (excited) electron configurations are examined for both the system global description and for the case of its partitioning into mutually closed subsystems, e.g., reactants. The chemical potential discontinuity for the integer numbers of electrons at zero temperature is stressed, and the KS orbital description of the charge transfer (CT) between reactants is discussed. Using the appropriate ensemble formulation of the KS theory the in situ chemical potential/electronegativity difference, the driving "force" behind the inter-reactant CT, is linked to the relevant KS frontier eigenvalues of polarized reactants.

1779-1791

Exploring Bonding Patterns of Molecular Systems Using Quantum Mechanical Bond Multiplicities

by J. Mrozek1, R.F. Nalewajski1 and A. Michalak2
1K. Guminski Department of Theoretical Chemistry, Jagiellonian University,
R. Ingardena 3, 30-060 Cracow, Poland
2Department of Computational Methods in Chemistry, Jagiellonian University,
R. Ingardena 3, 30-060 Cracow, Poland

(Received March 27th, 1997; accepted June 30th, 1997)

One of the fundamental chemical concepts, the structural formula of a chemical species, which visualizes bonding patterns in a given molecular system, can also be given a more flexible and quantified form in terms of alternative quantum-mechanical measures of bond-orders. The recently developed difference approach, based upon the one-determinantal wavefunction [Hartree-Fock (HF) and Kohn-Sham (KS) theories], compares the charge-and-bond-order matrix in a molecule (P) and that in the separated atoms limit (P0, SAL) defined in the orthogonal basis set of atomic functions. In this approach the atomic and diatomic contributions to the molecularly averaged difference between these matrices, <P>/2 = 1/2tr[P(P0 - P)], are used to define bond multiplicities. The main purpose of this work is to examine the overall performance of such KS and HF bonding indices, when applied to the set of chemically well defined reference systems, and to use them to investigate bond-orders in more challenging molecules, which have recently been the subject of independent studies. Manifestations of changing bond ionicity by these effective bond-orders are examined for a series of diatomics. Some methodological aspects associated with alternative SAL choices are discussed and tested.

1792-1797

Theoretical Density Functional Studies of Tautomeric and Conformational Forms of N4-hydroxycytosine
and Its 5-fluoro and 5-methyl Derivatives

by G. Bakalarski1,2 and B. Lesyng2,3
1Department of Biophysics, Agriculture University, Rakowiecka 26, 02-528 Warsaw, Poland
2Interdisciplinary Centre for Mathematical and Computational Modelling,
Pawinskiego 5A, 02-106 Warsaw, Poland
3Department of Biophysics, Warsaw University, Zwirki i Wigury 93, 02-089 Warsaw, Poland

(Received May 20th, 1997, accepted July 4th, 1997)

Density functional (DFT) calculations at the BLYP/DNP and B3LYP/6-31G(d,p) levels were performed for amino and imino tautomers of N4-hydroxycytosine (HC), N4-hydroxy-5-fluorocytosine (5F-HC) and N4-hydroxy-5-methylcytosine (5Me-HC). Full optimization of the molecular skeleton and zero-point vibrational corrections computed at the B3LYP level were included in the energy analysis. The results are compared with ab initio MBPT(2)/6-31G(d,p)//HF/6-31G(d,p) calculations [1] performed for HC and 5F-HC. The DFT methods, and in particular the B3LYP approximation, predict properly the higher stability of the imino tautomers, and with lower computational costs reproduce very well the energy differences obtained using the conventional ab initio methods.

1798-1825

Electron Localization in Liquid Methanol.
Quantum Path-Integral Simulation

by W.M. Bartczak 1,2 and M. Sopek1,
1Institute of Applied Radiation Chemistry, Technical University of Lodz,
Lodz, Wroblewskiego 15, Poland
2Department of Theoretical Chemistry, University of Lodz, Lodz, Pomorska 149/153, Poland

(Received April 18th, 1997; revised June 26th, 1997, accepted July 4th, 1997)

An excess electron in liquid methanol at room temperature was studied using the method of Path-Integral Molecular Dynamics simulation.
A compact charge distribution of an excess electron, suggesting a localized electron state, was found. The charge distribution is centred in a cavity built of methanol according to the traditional picture of the solvated electron. Various radial distribution functions were calculated reflecting the correlations between the cavity centre or the electron charge density and the sites of the methanol molecule. The correlations are stronger than in the case of the hydrated electron. Interpretation of the radial distribution functions as well as the bond-angle distribution functions leads to a picture of 4 methanol molecules forming the solvation shell of the solvated electron. The molecules are oriented towards the centre of the electron density by the OH bonds. The coordination number of the solvated electron agrees with the conclusions from electron magnetic resonance experiments.

1826-1848

Multiple Electron Exchanges in Calculations
of Pairwise Nonadditive Contribution
to Trimer Interaction Energy

by V.F. Lotricha, K. Szalewicza and B. Jeziorskib
aDepartment of Physics and Astronomy, University of Delaware, Newark, DE 19716
bDepartment of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

(Received August 26th, 1997; revised October 7th, 1997; accepted October 7th, 1997)

The first order of the symmetry-adapted perturbation theory has been used to compute the pairwise nonadditive contribution to the exchange repulsion energy in the He3, Ne3, Ar2HF, and (H2O)3 trimers. The contributions from single and double electron exchanges, as well as from the cyclic permutations involving three electrons at a time, were calculated separately and compared with the accurate result involving all possible electron permutations. The intramonomer electron correlation was completely neglected and the Hartree-Fock determinants were used to represent the monomer wave functions. The importance of the resulting three-body contributions, which can be quadratic (single exchanges), cubic (three-electron cycles), and quartic (double exchanges) in a typical intermolecular overlap integral S, is studied for several geometrical configurations of the investigated systems. Whereas the S2 and S3 terms are important for all systems, the role of the S4 terms turns out to be very small for Ar2HF, large for the rare-gas timers at linear configurations, and appreciable for the water trimer. The higher than double exchanges (S5 and higher terms) are negligible for all systems except for the water trimer at very small intermonomer separations where the expansion in powers of S ceases to be useful. The nonadditivity of the so-called zeroth-order exchange energy, i.e., the difference between, the Heitler-London and the first-order energies, has also been investigated. The zeroth-order exchange energy contains only the S4 and higher terms and becomes significant when the S4 contribution to the first-order energy is important. The S2 and S3 contributions to the first-order exchange nonadditivity in the Ar2HF trimer agree well with the calculations of Cybulski and collaborators [J. Chem. Phys., 101, 10708 (1994), ibid., 106, 3301 (1997)] using their pseudo-dimer model.

1849-1857

Multiple Elliptical-Gaussian-Density Annealing
as a Tool for Finding the Most Stable Structures.
Application to Lennard-Jones Atomic Clusters

by J. Pillardy and L. Piela
Quantum Chemistry Laboratory, Department of Chemistry, University of Warsaw,
02-093 Warsaw, Pasteura 1, Poland

(Received April 10th, 1997; accepted April 15th, 1997)

Smoothing of the potential energy hypersurface is a promising way to reduce complexity of the original hypersurface, thus facilitating the search for the most stable configuration of a molecular system. Despite of the effort made in the last decade to find an efficient smoothing technique, a reliable and economical method is still sought. One of the powerful approaches is the Gaussian Density Method (GDA) of Straub and coworkers. In the method one solves the reduced Bloch equation that describes the evolution of the spatial part of the canonical density distribution, when the temperature changes. In the GDA method this distribution is assumed, for each atom, as a single three-dimensional isotropic Gaussian with the position and width changing according to known equations of motion, when the temperature changes. In the present paper we allow for a three-dimensional elliptical Gaussian distribution for each atom. Additionally, when in the course of lowering the temperature the anisotropy of the ellipse becomes large enough, the single Gaussian distribution for an atom may branch into two elliptical Gaussian distributions. Evolution in temperature of the new distributions for the system is calculated by solving for each of them the independent reduced Bloch equation. Finally, when the temperature reaches 0 K, one has a number of Gaussian distributions, each corresponding to a structure and (usually low) energy of the system. The method has been applied to the clusters of N argon atoms (N = 5,..., 33), the system serving usually as benchmark. Allowing for the anisotropy of the Gaussian distributions results in a remarkable increase of numerical stability.


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