Jules W. Moskowitz

Water Molecule Interactions

Accurate SCF calculations have been carried out to investigate the potential of interaction for pairs and triplets of water molecules. The most stable pair configuration involves a linear hydrogen bond of length ROO = 3.00 A and strength 4.72 kcal/mole. Three‐molecule nonadditivities are large in magnitude and vary in sign according to the hydrogen‐bond pattern involved. In both aqueous liquids and solids, the net trimer nonadditivity effect amounts to increased binding energy, decreased neighbor distance, and slightly enhanced tendency toward perfect tetrahedral coordination symmetry. The nonadditivity furthermore is inconsistent with the phenomenology of simple mutual electrostatic polarization between neighboring molecules.

One‐Electron Properties of Near‐Hartree–Fock Wavefunctions. I. Water

Self‐consistent‐field calculations are reported for the ground state of the water molecule in a contracted and uncontracted Gaussian basis set. The uncontracted set is shown to be near the Hartree–Fock limit for water. One‐electron properties were computed from both wavefunctions. Our best estimates for several of these quantities are: dipole moment, μz = 1.995 D; quadrupole moment, θzz = − 0.108 and θxx = − 2.422 in buckinghams; octupole moment, Ωxxz = − 1.337 and Ωzzz = − 0.960 in units of 10−34 esu·cm3; average diamagnetic shielding at the proton, σAvd = 102.9 ppm; quadrupole coupling constant at the deuteron, (eqQ / h)AA = 343.9 kc/sec, and at the oxygen, (eqQ / h)aa = − 8.34 Mc / sec. The effect of including d‐type Gaussian functions in the basis is examined.

Correlated Monte Carlo wave functions for the atoms He through Ne

We apply the variational Monte Carlo method to the atoms He through Ne. Our trial wave function is of the form introduced by Boys and Handy. We use the Monte Carlo method to calculate the first and second derivatives of an unreweighted variance and apply Newton’s method to minimize this variance. We motivate the form of the correlation function using the local current conservation arguments of Feynman and Cohen. Using a self‐consistent field wave function multiplied by a Boys and Handy correlation function, we recover a large fraction of the correlation energy of these atoms. We give the value of all variational parameters necessary to reproduce our wave functions. The method can be extended easily to other atoms and to molecules.

One‐Electron Properties of Near‐Hartree–Fock Wavefunctions. II. HCHO, CO

The results of Hartree–Fock level self‐consistent‐field molecular orbital calculations using contracted Gaussian basis sets are reported for the ground states of the formaldehyde and carbon monoxide molecules. The best computed wavefunctions are shown to have total energies, at most, 0.05 a.u. from their Hartree–Fock limits. A large number of one‐electron properties were computed from the wavefunctions. Results for the carbon monoxide molecule are in excellent agreement with the Slater basis Hartree–Fock results of Huo [J. Chem. Phys. 43, 624 (1965)]. For formaldehyde the calculated molecular properties are in good agreement with experiment. Our best estimates for several of the properties in HCHO are: dipole moment, μz = 2.82 D; quadrupole moment, θaa = 0.0056 × 10−26 esu·cm2, θbb = 0.250 × 10−26esu·cm2, θcc = − 0.256 × 10−26esu·cm2; diamagnetic shielding at the proton, σaad(H) = 92.63 ppm, σbbd(H) = 94.68 ppm, σabd(H) = 52.80 ppm, σccd(H) = 147.13 ppm, and σAvd(H) = 111.48 ppm; diamagnetic shielding at ...

The electronic structure of small nickel atom clusters

The ground state electronic structure of small nickel atom clusters (Nin, n=1–6) has been calculated using the ab initio effective core potential self‐consistent field (SCF) method in a Gaussian expansion basis. The electronic configuration of the nickel atoms in the clusters is found to be very close to 3d94s1. The ground state electronic configurations for Nin generally have n unpaired 3d electrons in molecular orbitals (MO’s) spanning the same irreducible representations as the 4s atomic orbitals while the n 4s electrons fill their MO’s in accord with a simple three‐dimensional Huckel model with overlap. Exceptions to this description are found in the cases of linear systems where the 3d holes prefer δ over σ symmetry and in octahedral Ni6 where a different preferred set of 3d holes is obtained. The SCF ground state wave functions correspond roughly to a model in which the 3d electrons can be viewed as weakly interacting localized 3d9 units. The clusters are bound together primarily by the 4s electrons...

A new look at correlation energy in atomic and molecular systems. II. The application of the Green’s function Monte Carlo method to LiH

The potential energy surface of the LiH molecule is calculated using the Green’s function Monte Carlo method. The calculated correlation energy is 0.078±0.001 hartree and the binding energy is 2.56 eV. These results are within 6% and 2% of the experimental values, respectively. The Green’s function Monte Carlo method is discussed in some detail with particular emphasis on problems of chemical interest.

A molecular complex model for the chemisorption of hydrogen on a nickel surface

Abstract The chemisorption of hydrogen on nickel is studied using a localized surface complex: H 2 + Ni 2 → Ni 2 H 2 . The electronic structure was calculated using ab initio methods which included electron correlation, the core electrons of Ni being replaced by an ab initio quality effective potential. We find that the chemisorptive bond of H on Ni is formed primarily to the Ni 4s electron, the 3d electrons remaining localized on the individual Ni atoms. The dissociative chemisorption process is explained in terms of Woodward-Hoffmann correlation diagrams, with the d electrons allowing the reaction to occur on an otherwise forbidden reaction path involving a biradical Intermediate.

Conformational Analysis of Flexible Molecules: Location of the Global Minimum Energy Conformation by the Simulated Annealing Method

Abstract A new computational method for the location of the lowest energy conformation of flexible molecules is reported. The technique, called simulated annealing, is discussed and several applications are described.

Polarizabilities and Hyperpolarizabilities of Small Polyatomic Molecules in the Uncoupled Hartree–Fock Approximation

Near Hartree–Fock LCAO–MO–SCF contracted Gaussian wavefunctions are used to calculate the polarizabilities and hyperpolarizabilities of water, methane, carbon monoxide, and formaldehyde. The polarizabilities are shown to be in good agreement with the experimental data. In the case of water, an attempt was made to use the calculated hyperpolarizabilities to predict the line intensities and the depolarization ratio of a double quantum scattering experiment. Unfortunately, direct comparison with the actual experiment is premature at this time due to ambiguities in the interpretation of the experimental results.

Gaussian Wavefunctions for the 10‐Electron Systems. III. OH−, H2O, H3O+

A series of SCF calculations in a Gaussian basis are reported for the 10‐electron systems OH−, H2O, H3O+. For the most extensive basis, the total energy and dipole moment of H2O were computed to be −76.0421 and 0.782 a.u., respectively. The molecular geometry was explored for a variety of bases. In addition, the effect of polarization functions on the oxygen and the hydrogens was studied.