Claude A. Daul

Theoretical studies on the electronic properties and the chemical bonding of transition metal complexes using dft and ligand field theory

The research activity within our laboratory of computational chemistry at the University of Fribourg is presented. In this review, a brief outline of a recently proposed Ligand Field Density Functional Theory (LFDFT) model for single nuclear and its extension to dimer transition metal complexes is given. Applications of the model to dinuclear complexes are illustrated for the interpretation of exchange coupling in the bis-μ-hydroxo-bridged dimer of Cu(II) and to the description of the quadruple metal-metal bond in Re 2 Cl 8 2 - . The analysis of the chemical bonding is compared with results obtained using other approaches, i.e. the Extended Transition State model and the Electron Localization Function. It is shown that the DFT supported Ligand Field Theory provides consistent description of the ground and excited state properties of transition metal complexes.

DFT modeling of the relative affinity of nitrogen ligands for trivalent f elements: an energetic point of view

In many theoretical studies dealing with the selective complexation of trivalent actinides with respect to trivalent lanthanides, the method of calculation is assessed by comparing computed geometries with crystal structures that are often available. Yet, the selectivity is better rationalized through thermodynamic data, as enthalpy and entropy terms. In this article, we have theoretically modeled competing complexation reactions of [Ce(terpy)3]3+, [U(terpy)3]3+, [Ce(MeBTP)3]3+ and [U(MeBTP)3]3+ systems (terpy = 2,2′:6′2″-terpyridine; MeBTP = methyl-2,6-di(1,2,4-triazin-3-yl)pyridine) within the framework of the Density Functional Theory. Our calculations manage to qualitatively account for the experimental relative stabilities of terpy and MeBTP complexes, and in particular for the better coordinating strength of MeBTP for trivalent uranium. We also show by comparing the MeBTP ligand with its non-alkylated form (HBTP) that model systems often used in quantum chemistry must be carefully chosen when energetic comparisons are undertaken.

NON-EMPIRICAL DYNAMICAL DFT CALCULATION OF THE BERRY PSEUDOROTATION OF PF5

The pseudo rotation of PF5 has been investigated using both static and dynamic density functional theory (DFT) methods. The lowest energy path is the Berry pseudorotation, corresponding to the concerted exchange of two apical and two equatorial ligands. The potential energy surface has been derived and the transition state localised. In ab initio molecular dynamics the Berry pseudorotation has been observed and occurs with a typical period of 0.6 ps at 750 K. Analysis of the trajectories and comparison of the spectral density with the vibrational frequencies is presented.

Exchange energy gradients with respect to atomic positions and cell parameters within the Hartree-Fock Γ-point approximation

Recently, linear scaling construction of the periodic exact Hartree-Fock exchange matrix within the Gamma-point approximation has been introduced [J. Chem. Phys. 122, 124105 (2005)]. In this article, a formalism for evaluation of analytical Hartree-Fock exchange energy gradients with respect to atomic positions and cell parameters at the Gamma-point approximation is presented. While the evaluation of exchange gradients with respect to atomic positions is similar to those in the gas phase limit, the gradients with respect to cell parameters involve the accumulation of atomic gradients multiplied by appropriate factors and a modified electron repulsion integral (ERI). This latter integral arises from use of the minimum image convention in the definition of the Gamma-point Hartree-Fock approximation. We demonstrate how this new ERI can be computed with the help of a modified vertical recurrence relation in the frame of the Obara-Saika and Head-Gordon-Pople algorithm. As an illustration, the analytical gradients have been used in conjunction with the QUICCA algorithm [K. Nemeth and M. Challacombe, J. Chem. Phys. 121, 2877 (2004)] to optimize periodic systems at the Hartree-Fock level of theory.

Possible ring structures of armchair single-walled carbon nanotubes

Energetics and the electronic structure of various types of single-walled carbon nanotubes have been investigated by using Density Functional Theory. Armchair [n,n], zigzag [n,0] and chiral [n,m] C 40 H 20 nanotubes have been considered. Calculations show that the armchair isomer is the most stable among the three types and they further reveal the factors that stabilize this isomer. Nucleus-independent chemical shift calculations indicate the aromaticity of the individual hexagonal rings in the carbon nanotubes and explain the extent of electron delocalization in them.