Computational Inorganic and Analytical Chemistry

Our research activity in computational chemistry at the university of Fribourg is briefly presented including topics like: Electronic structure calculation of coordination compounds, density functional theory, multiplet structure calculation, modelling the optical and magnetic properties of metal complexes and inorganic materials, molecular dynamics, redox polymers, thin layer cells

Electronic fine structure calculation of metal complexes with three-open-shell s, d, and p configurations

The ligand field density functional theory (LFDFT) algorithm is extended to treat the electronic structure and properties of systems with three-open-shell electron configurations, exemplified in this work by the calculation of the core and semi-core 1s, 2s, and 3s one-electron excitations in compounds containing transition metal ions. The work presents a model to non-empirically resolve the multiplet energy levels arising from the three-open-shell systems of non-equivalent ns, 3d, and 4p electrons and to calculate the oscillator strengths corresponding to the electric-dipole 3dm → ns13dm4p1 transitions, with n = 1, 2, 3 and m = 0, 1, 2, …, 10 involved in the s electron excitation process. Using the concept of ligand field, the Slater-Condon integrals, the spin-orbit coupling constants, and the parameters of the ligand field potential are determined from density functional theory (DFT). Therefore, a theoretical procedure using LFDFT is established illustrating the spectroscopic details at the atomic scale that can be valuable in the analysis and characterization of the electronic spectra obtained from X-ray absorption fine structure or electron energy loss spectroscopies

Modeling the properties of open d-shell molecules with a multi-determinantal DFT

La théorie du champ des ligands a été utilisée avec succès durant des décennies pour décrire l’état fondamental et les états excités des complexes. Les chimistes utilisent cette théorie afin d’interpréter des spectres UV-Vis essentiellement. D’un autre côté, les chimistes computationels peuvent décrire assez précisément les propriétés correspondant à l’état fondamental mais les modèles permettant de décrire les propriétés des états excités sont encore en voix de développement. La méthode "Champ des Ligands - Théorie de la Fonctionnelle de la Densité", qui est la méthode présentée dans cette thèse, propose un lien entre la Théorie de la Fonctionnelle de la Densité (TFD) appliquée à l’état fondamental et la modélisation des propriétés des états excités par l’intermédiaire de la théorie du champ des ligands. Pour ce faire, nous calculons grâce à la TFD les énergies de tous les déterminants de Slater due à une configuration dn en référence a un état correspondant à une configuration moyenne (répartition égale des électrons d dans les 5 orbitales moléculaires correspondant aux orbitales d de l’élément de transition) afin de satisfaire aux exigences de la théorie du champ des ligands. Dans un premier temps, la méthode est appliquée à des composés connus afin de tester sa validité. Dans un deuxième temps, le champ d’application de la méthode est étendue à la modélisation des tenseurs g et A. Tout au long de cette thèse, les résultats obtenus sont comparés aux données expérimentales obtenues par les chimistes. Nous montrons aussi que la méthode donne plus d’informations que l’on ne pouvait espérer, en particuliers, lors du traitement des effets relativistes.Ligand field theory has been used along decades with success to describe ground and excited electronic states originating from dn transition metals complexes. Experimental chemists use such a theory to interpret spectra. On the opposite side, computational chemists can describe with good accuracy the ground states properties but models to calculate excited states properties are still being developed. The Ligand Field –Density Functional Theory, which is the method presented in this thesis, proposes a link between the density functional theory applied to ground state and the determination of excited states properties through the ligand field theory. To achieve this, we compute within the DFT formalism the energies of all the Slater determinants originating of a dn configuration taken as reference an average of configuration to satisfy the requirement of the Ligand Field Theory. In a first step, the method is applied to well known compounds to test the ligand field and Racah’s parameterization in comparison to values fitted from experimental UV-Vis spectra. Then we use a Ligand field program to predict the multiplet structure. Next, extension of the method is proposed to determine ESR parameters and relativistic effect within the same formalism. At each step, the results are compared to data which are well known for many decades by the chemists. We will also show the ability of the method to give more informations than usually expected

Geometry Optimization and Excited States of Tris(2,2'-bipyridine)ruthenium(ll) Using Density Functional Theory

During the last two decades, many investigations have been performed on molecules belonging to the family of tris(2,2'-bipyridine)ruthenium(II). In this work, a theoretical approach of the [Ru(bpy)3]2+ complex using Density Functional Theory and in particular the Amsterdam Density Functional (ADF) program package, is presented. The geometry of the [Ru(bpy)3]2+ complex has been optimized using the local density approximation (LDA). The optimization has been made within D3 symmetry and it leads to good agreement with the X-ray structure. As the photochemical and photophysical data suggest, two sets of low-lying empty molecular orbitals are found. In a first study, we dealt with the first set of levels, which correspond to Metal-to-Ligand Charge- Transfer states (MLCT), and calculated the positions of these MLCT states as well as the intensities of the transitions, using the Generalized Gradient Approximations (GGA). The results obtained are in good agreement with the experiment. In a second part, we focus on the upper set of unoccupied orbitals, which are metal-centered. Thus, we calculated the energy of the transition corresponding to the Lowest Ligand Field state, which has been suggested to be responsible for the photoracemization and photosubstitution

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 Re₂Cl₈²⁻. 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

Multiplets of free d- and f-metal ions: A systematic DFT study

In this work we apply in a systematic way our multi-determinantal model to calculate the fine structure of the whole atomic multiplet manifold. The key feature of this approach is the explicit treatment of near-degeneracy correlation using ad hoc configuration interaction (CI) within the active space of Kohn–Sham (KS) orbitals with open d- or f-shells. The calculation of the CI-matrices is based on a central symmetry decomposition of the energies of all single determinants (micro-states) calculated according to Density Functional Theory (DFT) for frozen KS-orbitals corresponding to the averaged configuration, eventually with fractional occupations, of the d- or f-orbitals and/or the direct calculation of the electrostatic reduced matrix elements (Racah or Slater–Condon parameters) occurring in the corresponding active space. We performed DFT calculations on all divalent and trivalent d²–d⁸ metal ions, as well as the f²–f¹² lanthanide(III) ions. We compare the results of both variants of the method with the data available in the literature. Both procedures yield multiplet energies with an accuracy of about hundred wave numbers and fine structure splitting accurate to less than a tenth of this amount

Improved coupled perturbed Hartree–Fock and Kohn–Sham convergence acceleration

A derivative version of the well-known direct inversion in the iterative subspace (DIIS) algorithm is presented. The method is used to solve the coupled perturbed Hartree–Fock (CPHF) equation to obtain the first and second derivatives of the density matrix with respect to an external electric field which, in this case, leads to the electric molecular polarizability and hyperpolarizability. Some comparisons are presented and the method shows good convergences in almost all cases

The effect of pressure on the structural and electronic properties of yttrium orthovanadate YVO4 compound: total-energy calculations

We have investigated the structural properties and electronic properties of the zircon-type and the scheelite-type YVO4 using first-principles method and by considering Engel-Vosko exchange correlation energy functional. The calculated lattice parameters and the atomic positions of the zircon-type YVO4 are in good agreement with the experiment. We also found from this study that YVO4 is stable in the zircon-type, and the calculated phase transition pressure from the zircon-type structure to the scheelite-type structure is about 5.92 GPa, which compares well with the experimental value of 7.5 GPa. From the density of states and band structures, the linearized augmented plane wave (LAPW) calculations indicate that the minimum band gap of YVO4 is located at the Γ point at the center of the Brillouin zone, for both phases. The calculated band gaps are 3.2 eV and 2.8 eV for the zircon-type phase and the scheelite-type phase, respectivel