Wolfram Koch

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.

The performance of density‐functional/Hartree–Fock hybrid methods: Cationic transition‐metal methyl complexes MCH+3 (M=Sc–Cu,La,Hf–Au)

Hybrid methods, including a mixture of Hartree–Fock exchange and density functional exchange‐correlation treatment have been applied to the cationic methyl complexes MCH+3 of the first and third‐row transition metals (M=Sc–Cu,La,Hf–Au). Bond dissociation energies and optimum geometries obtained with the ‘‘Becke‐Half‐and‐Half‐Lee–Yang–Parr’’ and ‘‘Becke‐3‐Lee–Yang–Parr’’ functionals and from calibration calculations employing quadratic configuration interaction with single and double excitations and with a perturbative estimate of triple excitations are reported. A comparison of the results for the 3d‐block species to earlier high‐level ab initio calculations and experimental data is carried out in order to assess the reliability of hybrid methods as a practical tool in organometallic chemistry. Furthermore, the bond dissociation energies of the cationic 5d‐block transition‐metal methyl complexes, many of which have not been investigated so far, are predicted.

The performance of density functional/Hartree-Fock hybrid methods: the bonding in cationic first-row transition metal methylene complexes

Abstract Density functional theory/Hartree-Fock hybrid methods have been applied to the cationic methylene complexes MCH 2 + of the first-row transition metals (M = Sc-Cu). A comparison of the computed results with earlier high-level ab initio MO calculations and experimental data is presented in order to assess the reliability of such hybrid methods as a practical tool in organometallic chemistry.

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.

On the use of koopmans' theorem to estimate negative electron affinities

Abstract For 26 molecules the experimentally determined negative electron affinities resulting from electron transmission spectroscopy are compared to the theoretically determined eigenvalues of the lowest unoccupied molecular orbitais (ϵ LUMO ) of the neutral compounds, and to the eigenvalues of the highest occupied molecular orbitals (ϵ HOMO ) of the respective anion. With the 3-21G and 6-31G * basis sets, the ϵ LUMO values are found to give qualitatively correct correlations in most, but not all, cases for molecules with similar structures. The ϵ LUMO data of the anions show a much poorer agreement with experimentally established trends. The inclusion of diffuse functions in the 6-31+G * basis set leads to a complete breakdown in the correlation of experimental and theoretical data.

Are there neutral helium compounds which are stable in their ground state?: A theoretical investigation of HeBCH and HeBeO

At the MP4(SDTQ)/6-311G★★//MP2/6-31G★★+ ZPE level of theory, HeBCH is predicted to be unstable towards helium dissociation by −6.0 kcalmol, but HeBeO is calculated to be a stable molecule by + 3.2 kcalmol. Convened to the reaction enthalpy, the latter value increases to + 3.9 kcalmol.

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...

Donor-acceptor interaction and the peculiar structures of dications.

Geometries et modes de liaison dans CH 2 X 2+ et CH 4 X 2+ avec X=FH, OH 2 , NH 3 , N 2 , F 2 , H 2 , CO, OC, CH 2 ( 1 A 1 ), CH 4

AN AB INITIO MOLECULAR ORBITAL STUDY OF THE STRUCTURES AND ENERGETICS OF THE NEUTRAL AND CATIONIC CUO2 AND CUNO MOLECULES IN THE GAS PHASE

The interactions of neutral and ionic copper atoms with molecular oxygen and nitric oxide have been examined by using relativistic effective core potentials (ECP) and different ab initio MO methods up to the coupled cluster CCSD(T) approach. For neutral CuO2 the ECP calculations reproduce the results of all‐electron calculations which prefer the ‘‘side‐on’’ structure by 0.9 kcal/mol versus an ‘‘end‐on’’ coordination. The binding energy for the ‘‘side‐on’’ complex (2A2) has been calculated to be 9.7 kcal/mol. For the cationic end‐on CuO+2 (3Σ+) an identical binding energy (9.7 kcal/mol) results from CCSD(T) calculations; the side‐on complex (3B1) is 4 kcal/mol less stable. The singlet state (1A’) of the cation is 27 kcal/mol higher in energy and bound with 13.6 kcal/mol with respect to singlet oxygen (1Δ+g) and Cu+ (1S), while the side‐on (1A1) state is 3.8 kcal/mol less stable than the 1A’ state. For the interaction of neutral Cu with NO the end‐on CuNO coordination (1A’) with a bonding energy of 10.4 kca...

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.