Attila Bérces

Analytic second derivatives of molecular energies: a density functional implementation

Abstract We report an implementation of analytic second derivatives with respect to nuclear displacements, based on density functional theory within the Kohn-Sham formalism. The implementation is in line with the Amsterdam Density Functional package ADF, and includes the use of numerical integration as well as the frozen core approximation. The efficiency of the algorithm is tested in comparison with finite difference methods.

An implementation of the coupled perturbed Kohn-Sham equations: perturbation due to nuclear displacements

Abstract The Coupled Perturbed Kohn-Sham equations have been implemented in the Amsterdam Density Functional program package. Our implementation differs from previous ones in many ways. This program uses density fitting to calculate the Coulomb and exchange integrals. Further, all matrix elements of the Fock type matrix and its derivatives are calculated by numerical integration. The frozen core approximation is also implemented. Our implementation is approximately 10 times faster than a finite difference algorithm, and the absolute CPU times also compare favorably with other reported implementations.

The harmonic force field of benzene. A local density functional study

The harmonic force field of benzene has been calculated by a method based on local density functional theory (LDF). The calculations were carried out employing a triple zeta basis set with triple polarization on hydrogen and double polarization on carbon. The LDF force field was compared to the empirical field due to Ozkabak, Goodman, and Thakur [A. G. Ozkabak, L. Goodman, and S. N. Thakur, J. Phys. Chem. 95, 9044 (1991)], which has served as a benchmark for theoretical calculations as well as the theoretical field based on scaled Hartree–Fock ab initio calculation due to Pulay, Fogarasi, and Boggs [P. Pulay, G. Fogarasi, and J. E. Boggs, J. Chem. Phys. 74, 3999 (1981)]. The calculated LDF force field is in excellent qualitative and very good quantitative agreement with the theoretical field proposed by Pulay, Fogarasi, and Boggs as well as the empirical field due to Ozkabak, Goodman, and Thakur. The LDF field is closest to the values of Pulay and co‐workers in those cases where the force constants due to...

Application of density functional theory to the calculation of force fields and vibrational frequencies of transition metal complexes

In the last five years we have applied density functional theory to gain information about the harmonic force fields, vibrational frequencies and IR intensities of transition metal complexes. This paper is the summary of the outcome of this series of investigations. We discuss the calculation procedures with special emphasis on the effect of reference geometry and exchange correlation potential. We also include our benchmark test calculation of the benzene force field. We discuss the major findings of our force field studies of transition metal complexes: ferrocene, debenzene-chromium, benzene-chromium tricarbonyl, and transition metal carbonyls. We found numerous miss assignments in the experimental spectra. We investigated how the force constants of aromatic rings change upon complexation, and we provide explanations for these changes based on qualitative orbital analysis.

The harmonic force field of benzene calculated by local density functional theory

Abstract Density functional (DF) calculations have been carried out on the in-plane harmonic frequencies and valence force field of benzene. The calculated force constants are in excellent qualitative agreement with previous scaled ab initio forcefields. Harmonic frequencies are predicted with an average deviation of 16.7 cm −1 (1.5%) for the frequencies, not including CH stretching modes. The present study is at variance with a previous DF investigation of Albertazzi and Zerbetto, where the calculated force constant differed considerably from those obtained by scaled ab initio methods.