Roland H. Hertwig

On the parameterization of the local correlation functional. What is Becke-3-LYP?

Abstract It was found that the results of B3LYP calculations are not consistent throughout different implementations of this HF/DFT hybrid functional. The origin of this discrepancy lies in the two different formulations of the VWN local correlation functional, and it depends on the program which one is incorporated in the B3LYP functional. A comparison between the two different flavors of the VWN local correlation functional is made and the question as to which one is more accurate is addressed.

On the accuracy of density functionals and their basis set dependence: An extensive study on the main group homonuclear diatomic molecules Li2 to Br2

The equilibrium bond distances, harmonic frequencies, and bond dissociation energies of the 21 homonuclear diatomics Li2—F2, Na2—Cl2, and K2—Br2 have been determined using approximate density functional theory (DFT) employing various widely used functionals and basis sets ranging from single zeta to triple zeta plus polarization quality. The results are in general much less sensitive to the size of the basis set as in conventional ab initio molecular orbital (MO) theory, while the choice of the functional is of much more significance. For one basis set (6‐311G*), the performance of the DFT‐based calculations has been compared and found to be superior to Hartree‐Fock (HF) Møller Plesset second order perturbation theory (MP2), or configuration interaction with single and double excitations (CISD) calculations. Particularly, no pathological cases, such as the group 2 dimers (Be2, Mg2, Ca2), are observed.

How do coinage metal ions bind to benzene

The interaction of the metal ions Cu+, Ag+, and Au+ with a benzene molecule has been investigated employing various quantum chemical strategies such as density functionals, Hartree—Fock, second-order perturbation theory and coupled cluster techniques. The three coinage metal cations show interesting differences in their preferred site of complexation with the π system of benzene. Cu+ prefers a highly symmetric η6 arrangement. In the Ag+—C6H6 complex the metal ion can change its position above the whole π plane of benzene virtually barrier free. For Au+ the calculations predict as favoured site of complexation a position above the carbon backbone, i.e., at the periphery and not in the centre of the benzene ring. Unlike copper or silver, this latter site of complexation is significantly less stable in the case of gold. At our most sophisticated level of theory, the computationally predicted binding energies agree well with the experimental numbers for the copper and silver complexes. For the gold complex on...

The metal-ligand bond strengths in cationic gold(I) complexes. Application of approximate density functional theory

Abstract The cationic gold(I) complexes Au+(L) with L = H2O, CO, C2H4, NH3, C3H6 and C6H6 have been examined employing approximate density functional theory at the local spin density level augmented with gradient corrections for exchange due to Becke and for correlation due to Perdew and Lee, and Yang and Parr, and using relativistic pseudopotentials for the gold cation. The predicted order of bond strengths is in agreement with gas-phase ligand exchange reactions. In particular, contrary to our previous findings using conventional ab initio MO methods (MP2 and CCSD(T)) and a density functional/Hartree-Fock hybrid method (B3LYP), the calculated gold-ligand binding energy of Au+(NH3) exceeds the binding energy of Au+(C2H4), in accord with the experimentally obtained order of gold-ligand stabilities.

Towards an accurate gold carbonyl binding energy in AuCO+: Basis set convergence and a comparison between density functional and conventional methods

The binding energy of the ground-state AuCO+ molecule has been systematically investigated using quantum chemical methods such as various density functionals and correlated wave function based approaches like second order Mo/ller–Plesset perturbation and the coupled cluster ansatz with perturbative treatment of triple excitations. These were combined with a total of 14 relativistic effective core potential/valence and all-electron basis sets of increasing flexibility for gold and CO, respectively. Special emphasis is paid to the role of the basis set superposition error and the relevance of different ways to improve the one particle basis sets. A significant effect on the basis set superposition error is observed in the density functional schemes upon enlarging the valence basis sets.

Economical treatments of relativistic effects and electron correlation in WH6

The equilibrium geometries and relative stabilities of several structural isomers of tungsten hexahydride, WH6, have been obtained at different levels of quantum chemical calculations. The performance of various strategies to (i) include electron correlation, viz. density functional theory based approaches, Møller/Plesset perturbation and coupled cluster theory, and to (ii) account for scalar relativistic effects, viz. various relativistic effective core potentials, first order perturbation theory, a quasi‐relativistic treatment employing a Pauli Hamiltonian, and use of the Douglas/Kroll operator, are compared to the best theoretical data available. It is shown that relativistic and electron correlation effects are most important for the high‐symmetry species, that these effects give rise to opposite trends in relative energies, and that overall the relativistic effects dominate. The most efficient way to incorporate relativistic effects appears to be via the use of relativistic effective core potentials, while the correlation energies are best taken account of using a conventional method such as CCSD(T). © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1604–1611, 1998