A. van der Avoird

Density functional calculations of molecular hyperfine interactions in the zero order regular approximation for relativistic effects

Expressions are derived within the relativistic regular approximation (ZORA) for the evaluation of the magnetic hyperfine interactions in paramagnetic molecules. For hydrogen-like atoms exact first order relations between the ZORA and Dirac formalism are given for the calculation of g- and A-tensors. Density functional calculations are performed on the neutral atoms Cu, Ag and Au, on some small test molecules NO2, HCO, and TiF3, and on some paramagnetic clusters consisting of 5 or 7 atoms of the group IB metals: Cu7, Cu2Ag5, CuAg6, Ag5, Ag7, and Au7. It is shown that the calculated ESR parameters of the heptamers are in good agreement with results of experiments, which originally were assigned to pentamers.

Density functional calculations of molecular g-tensors in the zero order regular approximation for relativistic effects

A method has been developed for the calculation of the g-tensor of Kramers doublet open shell molecules, which uses the spinor of the unpaired electron of the paramagnetic molecule, obtained from a density functional calculation. Spin–orbit coupling is taken into account variationally using the zeroth-order regular approximation (ZORA) to the Dirac equation. The problem of gauge dependence is solved by using gauge including atomic orbitals (GIAO’s). The method gives fair agreement with experimental values for the g values of some small test molecules NO2, HCO, and TiF3.

Quantum dynamics of non-rigid systems comprising two polyatomic fragments

We combine earlier treatments for the embedding of body-fixed coordinates in linear molecules with the close-coupling formalism developed for atomdiatom scattering and derive a hamiltonian which is most convenient for describing the nuclear motions in van der Waals complexes and other non-rigid systems comprising two polyatomic fragments, A and B. This hamiltonian can still be partitioned in the form HA + HB + HINT , just as the space-fixed hamiltonian. The body-fixed form, however, has several advantages. We discuss solution strategies for the rovibrational problem in non-rigid dimers, based on this partitioning of the hamiltonian. Finally, in view of the size of the general polyatomic-polyatomic case, we suggest problems which should be currently practicable.

Ab initio studies of the interactions in Van der Waals molecules

2 Mechanisms of Van der Waals Interactions; Distance and Orientational Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Distance and orientational dependence 4 2.2 Model potentials 6 2.3 Contributions to the interaction energy 8 2.3.1 Electrostat ic; long range mult ipole interactions, penetrat ion effects 8 2.3.2 Induct ion, dispersion; muit ipole interactions, penetra t ion effects 10 2.3.3 Exchange . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4 Interact ions from supermolecule calculations . . . . . . . . . . . . 13 2.5 Addi t iv i ty . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Multipole moments, polarizabilities and anisotropic long range interaction coefficients for N2

This paper contains results for the permanent multipoles, the multipole polarizabilities and the related anisotropic long range interaction coefficients C 5 to C 10 (complete) for the nitrogen molecule. The electrostatic, induction and dispersion interaction coefficients have been calculated using ab initio SCF wavefunctions; better estimates for the dispersion terms have been obtained by an approximate procedure, which uses the accurate (semi-) empirical data available for C 6 and the dipole polarizability, in combination with the ab initio results. The pure quadrupole-quadrupole anisotropy appears to be substantially modified by the dispersion anisotropy and, to a smaller extent, by the higher multipole electrostatic interactions; the induction energy can be neglected. The dispersion anisotropy factors γ8 and γ10, are much larger than γ6, due to the occurrence of the (completely anisotropic) mixed-pole terms. The recently proposed non-empirical Unsold method yields results which support applications to ...

An improved intermolecular potential for nitrogen

Using new ab initio calculations for the multipole and short range interactions and the results for the dispersion interactions recently calculated in our institute, we have constructed a new intermolecular potential for nitrogen. Its distance and angular dependence is expressed analytically in a spherical expansion. The long range dispersion interactions have been damped for charge penetration and exchange effects via the parameter‐free damping functions of Tang and Toennies, generalized to the case of an anisotropic potential, and we have introduced two scaling constants in the short range repulsion in order to obtain a second virial coefficient that lies within the experimental error in the entire temperature range. The use of the new potential in lattice dynamics calculations yields good results for several properties of solid nitrogen.

An ab initio intermolecular potential for the carbon monoxide dimer (CO)2

We have constructed an analytical potential energy surface for CO–CO by means of ab initio calculations for the electrostatic and first‐order exchange interactions and by the use of accurate dispersion coefficients recently calculated in our group. Parameter‐free damping functions account for second‐order exchange and penetration effects. The anisotropy of this potential is represented by an expansion in spherical harmonics for the molecules A and B, up to LA, LB=5 inclusive. The second virial coefficients calculated with this potential, including quantum corrections, lie within the experimental error bars over a wide temperature range.

LCAO studies of hydrogen chemisorption on nickel: I. Tight-binding calculations for adsorption on periodic surfaces

Abstract The model we have used to study hydrogen chemisorption on nickel surfaces is a tightbinding Extended Huckel method applied to finite (periodic) crystals up to about 250 atoms, the non-orthogonal basis set comprising five 3d orbitals, one 4s orbital and three 4p orbitals per atom. After calculating the band structure of fcc nickel, we have examined, by this model, the effect of the (100), (110) and (111) surfaces on the local density of states and the charge distribution. The results agree closely with moment calculations of the density of states in semi-infinite crystals and with experimental (XPS, UPS and INS) spectra. Extensive studies have been made of the influence of adsorption on the (partial) densities of states in order to illuminate the nature of the chemisorption bond. Particularly, we have concluded that both the 3d electrons and the conduction electrons take part in this bond. Equilibrium positions for adsorption on various sites have been determined and the adsorption energy has been computed and compared with experimental data. We find that the stability of adsorption decreases in the order (110) > (100) > (111) and Atop > Bridge > Centred.

Molecular orbital models for hydrogen adsorption on different sites of a nickel crystal

Abstract Model calculations for the chemisorption of hydrogen atoms on nickel (111), (100) and (110) surfaces are carried out by means of the Extended Huckel MO method. After comparison of the results obtained on a cluster of 13 nickel atoms with the properties of the metal, adsorption at different surfaces was studied by truncating this cluster and adsorbing a hydrogen atom on it, so that the environment of the adsorption site has the correct symmetry. It can be concluded that the adsorption of a hydrogen atom over a surface nickel atom is energetically more favourable than adsorption in some surface holes. Also the surface potential is more negative in the first case. The adsorption energy decreases with an increasing number of neighbours to the surface atom. It appeared further that the structure of the “surface molecule” is more important for determining which d-orbitals play a role in chemisorption than is the interaction with the “bulk” metal atoms. Moreover, we found that the 4s Orbitals are very important for covalent adsorption. Although the chemisorption of hydrogen atoms on copper is of a different type (the 3d orbitals not being involved), the greater binding to the 4s orbitals causes the adsorption energy to be comparable with the nickel case.

Dynamics of molecular crystals

Publisher Summary This chapter illustrates the dynamics of molecular crystals. The intramolecular vibrations and intermolecular vibrations (usually called lattice vibrations) are discussed. Because the chapter deals with molecules, two types of lattice vibrations can be distinguished; translational and rotational. In order to describe these motions, the potential energy of the crystal is expressed as a function of the center of mass positions and the orientations of all molecules. The chapter provides a detailed description of the different ways in which the potential can be expressed, each way having its own merits, depending on the subsequent calculations in which it has to be used. Later, the chapter briefly discusses the harmonic and quasi-harmonic models that are commonly used to describe the molecular motions— that is, the lattice vibrations, in molecular crystals. A description of perturbation theory around the harmonic model and of the self-consistent phonon method is also presented. The dynamical models for large-amplitude motions are also presented.