Jan Andzelm

A generalized synchronous transit method for transition state location

Abstract This paper describes a generalized synchronous transit method for locating transition state structures or first-order saddle points. The algorithm is based on the established scheme of combining the linear or quadratic synchronous transit method with conjugate gradient refinements but generalized to deal with molecular and periodic systems in a seamless manner. We apply the method to a study of the early stage atomic layer deposition (ALD) growth of ZrO2.

Incorporation of solvent effects into density functional calculations of molecular energies and geometries

In this paper, we present the implementation of the ‘‘conductorlike screening model’’ (COSMO) into the density functional program DMol. The electronic structure and geometry of the solute are described by a density functional method (DFT). The solute is placed into a cavity which has the shape of the solute molecule. Outside of the cavity, the solvent is represented by a homogeneous dielectric medium. The electrostatic interaction between solute and solvent is modeled through cavity surface charges induced by the solvent. The COSMO theory, based on the screening in conductors, allows for the direct determination of the surface charges within the SCF procedure using only the electrostatic potentials. This represents the major computational advantage over many of other reaction field methods. Since the DMol/COSMO energy is fully variational, accurate gradients with respect to the solute coordinates can be calculated for the first time, without any restriction on the shape of the cavity. The solvation energi...

Spin contamination in density functional theory

Abstract Local density functional calculations on a series of small, neutrals radicals demonstrate that the unrestricted Kohn-Sham wave-function is much less contaminated by higher spin states than its unrestricted Hartree—Fock couterpart, even for radicals which exhibit major contamination in their standard UHF wavefunction. A study of the dissociation curves for the OH and CN radicals shows that the UKS wavefunction remains essentially spin pure out to about 1.5 times the equilibrium bond length. Some general observations regarding spin contamination in unrestricted SCF wavefunctions are presented.

THE EFFECT OF GRID QUALITY AND WEIGHT DERIVATIVES IN DENSITY FUNCTIONAL CALCULATIONS

Full density functional geometry optimizations on hydrogen peroxide and heptane/dimethyl pentane using six different numerical grids are presented. The grids vary in quality and gradients are calculated (1) assuming a fixed grid and no weight derivatives, and (2) with full allowance for a ‘‘moving’’ atom‐centered grid and inclusion of the weight derivatives. The results clearly demonstrate that accurate energies and geometries can be obtained with around 3500 points per atom for medium‐sized systems (up to say 30 atoms) without the necessity of including the weight derivatives. The latter only begin to influence the results for grids which are of insufficient quality to guarantee reliable values in any case.