| Summary: | This thesis presents the Effective Hamiltonian of Crystal Field (EHCF) method, a hybrid quantum chemical method developed for an accurate treatment of strongly correlated d-shells of transition metal atoms embedded into periodic
systems. The main emphasis is made on the quantitative description of local d-d (crystal field) electronic transitions. EHCF is based on dividing a space of one-electron states in two subspaces separately spanned by d- and s,p-atomic orbitals. The many-electron wave function of the correlated d-system is expressed in the configuration interaction form, while the s,p-subsystem is described by the single-reference wave function. Resonance interactions between subsystems are considered by the Löwdin partitioning technique combined with the Green function formalism.
The test results for a series of transition metal (TM) oxides and TM dopants in oxide materials demonstrate the ability of EHCF to accurately reproduce the spin multiplicity and spatial symmetry of the ground state as well as energies and multiplicities of the excited d -states. For the studied materials, the calculated d -d transitions agree with the lines observed in optical spectra. For iron-containing compounds our calculations allow to reproduce values and temperature dependence of 57 Fe Mössbauer quadrupole splitting observed in experiment.
We apply EHCF to investigate carbodiimides and hydrocyanamides of transition metals, three-dimensional metal-organic frameworks (MOFs) including spin crossover in MOFs, chromium (III) dopants in wide gap materials suitable
for optical and quantum computing applications. We discuss future perspectives of the EHCF method and its place in the context of modern solid-state quantum chemistry and physics.
Further development of this thesis is related to single-atom TM catalysts. We apply EHCF to study the electronic structure of iron (II) and nickel (II) catalysts supported on the nitrogen-doped carbon surface. Additionally, we pro-
pose a kinetic theory describing nucleation and formation of stable single atoms of transition metal on the surface with point defects in the physical vapour deposition process. Our analysis shows how the ratio of surface density of single atoms and nanoclusters (SA:NC) depends on experimental conditions and metal-support interactions. This analysis is tested against experimental data on magnetron sputtering deposition of platinum on hexagonal boron nitride
(h-BN) surface. We show that the proposed kinetic theory allows to reproduce the observed values of the mean diameter of nanoclusters and qualitative trends in the dependence of the SA:NC ratio on the experimental conditions.
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