Taras Petrenko

• University of Stuttgart

For larger molecules, the computational demands of configuration selective vibrational configuration interaction theory (cs‐VCI) are usually dominated by the configuration selection process, which commonly is based on second order vibrational Møller‐Plesset perturbation (VMP2) theory. Here we present two techniques, which lead to substantial accele...

Vibrational configuration interaction calculations (VCI) have been performed to study the impact of the nature of the underlying coordinate systems, i.e., canonical vs localized normal coordinates, on accurate vibrational structure calculations for non-Abelian molecules. Once the correlation space is represented by real-valued primitive Hartree pro...

Nitrogen doped SiC nanoclusters of various shape and polytype structurescwere modelled in the framework of the density functional theory using the PBE0 hybrid functional. While in the bulk crystal N C ...

The time-independent eigenstate-free Raman wavefunction approach for calculating anharmonic vibronic spectra has been extended for the calculation of Herzberg–Teller contributions on the basis of an n-mode expansion of the transition electric dipole moment surface. This allows for the efficient simulation of Franck–Condon dark vibronic spectra. In...

The time-independent eigenstate-free Raman wavefunction approach, which is based on the vibrational inhomogeneous Schrödinger equation (ISE), is a promising alternative to the well-known sum-over-states and time-dependent methods for the calculation of optical bandshapes and resonance Raman intensities. The solution of the ISE, the Raman wavefuncti...

The X̃ 2A2←X̃ 1A1 photoelectron spectrum of furan has been studied by a time-independent eigenstate-free Raman wave function approach based on multi-dimensional potential energy surfaces obtained from explicitly correlated distinguishable clusters calculations. Individual vibronic transitions with the most significant Franck-Condon factors were det...

Due to a low lying fragmentation channel the X2B1 <- X1A1 photoelectron spectrum of difluoromethane is dominated by strong anharmonicity effects. We have used a time-independent eigenstate-free Raman wave function approach (RWF) to calculate the entire spectrum. Vibronic transitions with the most significant Franck-Condon factors were determined by...

Vibrational configuration interaction theory is a common method for calculating vibrational levels and associated IR and Raman spectra of small and medium-sized molecules. When combined with appropriate configuration selection procedures, the method allows the treatment of configuration spaces with up to 10¹⁰ configurations. In general, this approa...

In this paper, we present a detailed study of the boron impurity in 3C-SiC (BSi) in the cluster (CL) and supercell (SC) approximations, using representative local, gradient-corrected, and hybrid density functionals. Comparison of the theoretical spin-Hamiltonian parameters, calculated in the CL approximation using nonlocal density functionals, with...

The calculation of vibronic spectra and resonance Raman intensities can be performed on the basis of the Raman wavefunction (RWF) formalism. In general, the well-known sum-over-states (SOS) and time-dependent methods can be applied for calculating the RWF. We present an alternative route in which the RWF is determined pointwise in a spectral range...

In this paper, various implementations of the analytic Hartree-Fock and hybrid density functional energy second derivatives are studied. An approximation-free four-centre implementation is presented, and its accuracy is rigorously analysed in terms of self-consistent field (SCF), coupled-perturbed SCF (CP-SCF) convergence and prescreening criteria....

One is enough! The changes of the electronic structure induced by the adsorption of water and ammonia in the catalyst titanium silicalite-1 (TS-1) are investigated by means of (resonant) valence-to-core X-ray emission spectroscopy. Based on spectra simulations using density functional theory it is concluded, contrary to the widely accepted view, th...

In this work, an improved method for the efficient automatic simulation of optical band shapes and resonance Raman (rR) intensities within the "independent mode displaced harmonic oscillator" is described. Despite the relative simplicity of this model, it is able to account for the intensity distribution in absorption (ABS), fluorescence, and rR sp...

Hydrogenase proteins catalyze the reversible conversion of molecular hydrogen to protons and electrons. While many enzymatic states of the [NiFe] hydrogenase have been studied extensively, there are multiple catalytically relevant EPR-silent states that remain poorly characterized. Analysis of model compounds using new spectroscopic techniques can...

Multiple spectroscopic and computational methods were used to characterize the ground-state electronic structure of the novel {CoNO}(9) species Tp*Co(NO) (Tp* = hydro-tris(3,5-Me(2)-pyrazolyl)borate). The metric parameters about the metal center and the pre-edge region of the Co K-edge X-ray absorption spectrum were reproduced by density functional...

The underlying physics and analysis of Mössbauer spectra have been explained in detail in Chap. 4. In that chapter, the principles of how a spectrum is parameterized in terms of spin-Hamiltonian (SH) parameters and the physical origin of these SH parameters have been clarified. Many Mössbauer studies, mainly for 57Fe, have been performed and there...

In this paper, we present the implementation of efficient approximations to time-dependent density functional theory (TDDFT) within the Tamm-Dancoff approximation (TDA) for hybrid density functionals. For the calculation of the TDDFT/TDA excitation energies and analytical gradients, we combine the resolution of identity (RI-J) algorithm for the com...

A systematic study of 12 ferric and ferrous Kbeta X-ray emission spectra (XES) is presented. The factors contributing to the Kbeta main line and the valence to core region of the spectra are experimentally assessed and quantitatively evaluated. While the Kbeta main line spectra are dominated by spin state contributions, the valence to core region i...

The three square planar complexes [N(n-Bu)(4)](2)[Cr(II)L(2)] x 4 CH(3)CN (S = 2; 1), [N(n-Bu)(4)][Co(III)L(2)] (S = 1; 3), and [N(n-Bu)(4)](2)[Rh(II)L(2)] x 4 CH(3)CN (S = 1/2; 4) have been prepared and structurally characterized by X-ray crystallography (L(2-) represents the 3,6-bis(trimethylsilyl)benzene-1,2-dithiolate(2-)). Aerial oxidation of...

Twelve structural models for the S(2) state of the oxygen-evolving complex (OEC) of photosystem II are evaluated in terms of their magnetic properties. The set includes ten models based on the 'fused twist' core topology derived by polarized EXAFS spectra and two related models proposed in recent mechanistic investigations. Optimized geometries and...

Exchange coupling parameters and isotropic (55)Mn hyperfine couplings of fourteen mixed-valence Mn(III)-Mn(IV) dimers are determined using broken-symmetry density functional theory (DFT) and spin projection techniques. A systematic evaluation of density functional approaches shows that the TPSSh functional yields the best exchange coupling constant...

The reliable correlation of structural features and magnetic or spectroscopic properties of oligonuclear transition-metal complexes is a critical requirement both for research into innovative magnetic materials and for elucidating the structure and function of many metalloenzymes. We have developed a novel method that for the first time enables the...

Tetracene (Tc) and rubrene (Rub) are two prototype fluorescent molecules. Both molecules exhibit the same 'fluorescent backbone', but due to the additional phenyl groups, the backbone of Rub is twisted, whereas it is planar for Tc. In agreement with earlier investigations, optical spectroscopy of the respective solutions reveals that the S0→S1 tran...

Iron K-edge X-ray absorption pre-edge features have been calculated using a time-dependent density functional approach. The influence of functional, solvation, and relativistic effects on the calculated energies and intensities has been examined by correlation of the calculated parameters to experimental data on a series of 10 iron model complexes,...

The Cl K-edge spectra of a series of metal tetrachloride complexes have been simulated using a simple TD-DFT based protocol. The influence of the chosen density functional, relativistics, basis set, and solvation has been systematically investigated. The results show that good agreement between the calculated spectra and the relative experimental e...

A general method for the simulation of absorption (ABS) and fluorescence band shapes, resonance-Raman (rR) spectra, and excitation profiles based on the time-dependent theory of Heller is discussed. The following improvements to Heller's theory have been made: (a) derivation of new recurrence relations for the time-dependent wave packet overlap in...

The characterization of high-valent iron species is of interest due to their relevance to biological reaction mechanisms. Recently, we have synthesized and characterized an [Fe(V)-nitrido-cyclam-acetato]+ complex, which has been characterized by Mössbauer, magnetic susceptibility data, and XAS spectroscopies combined with DFT calculations (Aliaga-A...

A series of transition metal complexes involving non-innocent o-dithiolene and o-phenylenediamine ligands has been characterized in detail by various spectroscopic methods like magnetic circular dichroism (MCD), absorption (abs), resonance Raman (rR), electron paramagnetic resonance (EPR), and sulfur K-edge X-ray absorption spectroscopies. A comput...

We present a 'first-principles' methodology for the calculation of the parameters that are required for the simulation of nuclear resonance vibrational spectra (NRVS) of molecular systems. Formulae are given for the intensities of vibrational transitions corresponding to the so-called single-and double-phonon contributions to the NRVS signal. The m...

In this review some advanced aspects of the theoretical methods for the calculation of transition metal optical spectra with ab initio methods are discussed. Density functional theory (DFT) based methods are not covered. A brief introduction into the field of complete active space self-consistent field (CASSCF) calculations is provided. These metho...

Transition metal complexes involving the benzene-1,2-dithiol (L(2-)) and Sellmann's 3,5-di-tert-butylbenzene-1,2-dithiol(L(Bu 2-)) ligands have been studied by UV-vis, infrared (IR), and resonance Raman (rR) spectroscopies. Raman spectra were obtained in resonance with the intervalence charge transfer (IVCT) bands in the near-infrared region and li...

The Ky1 , Ky2 , and Ky3 centers are the dominant defects produced in the electron-irradiated p -type 6H-SiC crystals. The electron paramagnetic resonance study of these defects has been performed in the temperature range of 4.2-300K at X , K , and Q bands. The centers are characterized by the fourfold silicon coordination established on a basis of...

A cluster calculation of hyperfine coupling constants based on density functional theory (DFT) has been performed for the carbon 100 split interstitial (V C + 2C) in various charge and spin states in cubic SiC along with the dihydrogen-containing defect (V C + 2H). Compared to the isolated carbon vacancy, the presence of two carbon atoms in the spl...

The molecular structures, harmonic frequencies, absolute infrared intensities and Raman scattering activities have been calculated for metal triiodides, MI3 (M=As, Sb, Bi) with the use of hybrid density functional (mPW1PW and B3LYP) and ab initio (HF and MP2) methods. The theoretical results are compared with the available experimental data and oth...

The equilibrium geometry and hyperfine interaction constants of the nearest and next-to-nearest neighbor atoms are calculated for a negatively charged silicon vacancy in the high-spin state in cubic SiC. The calculations are performed within the cluster approach in terms of the density-functional theory (DFT). It is shown that the results of calcul...

A brief review is given on EPR study of irradiation-induced defects in SiC. The results of low-temperature study of Ky1 and Ky2 centers reveal for both of them the CS symmetry, spin and close coincidence of the g-tensor components. For Ky2 defect the principal values of g-tensor have been determined as gz=2.0048, gx=2.0022 and gy=2.0037, where z an...

Cluster calculation of carbon and silicon vacancies in cubic SiC has been performed for the charge states of +1, 0 and −1 and possible spin states. The density functional theory has been used with the B3LYP exchange-correlation functional and Gaussian basis set applied to the 52- and 70-atom clusters. Being suitable for a comparison with EPR data,...

The low-temperature X-band EPR study of Ky1 and Ky2 centers assigned to positively charged carbon vacancy (VC+) in two quasicubic sites of 6H-SiC crystal is presented. The CS symmetry, spin /S=1/2 and close coincidence of the g-tensor components have been revealed. The principal values of g-tensor are determined as gz=2.0048, gx=2.0022 and gy=2.003...

Theoretical simulation of hyperfine parameters for the nearest and next-nearest neighbor atoms of VC+ in SiC has been performed for the cubic and hexagonal clusters. The gradient-corrected all-electron DFT calculations with Becke's three-parameter functional have been performed by the use of split valence basis of Gaussian functions with d-function...

The results of a comprehensive study by the methods of IR absorption, Raman scattering, photoluminescence (PL), and electron spin resonance (ESR) of SiOx films prepared by thermal evaporation of SiO in a vacuum are presented. The nature of structural transformations occurring on annealing the films is determined. Annealing in the temperature range...

The EPR spectra produced in boron-doped 6H-SiC by 2 MeV electron irradiation are described. Three axially symmetric near 77 K spectra Ky1 with g∥1 = 2.0035 and g⊥1 = 2.0041, Ky2 with g∥2 = 2.0028 and g⊥2 = 2.0046, Ky3 with g∥3 = 2.0024, g⊥3 = 2.0048 and with relatively strong hyperfine splittings have been detected. Based on the intensity ratio of...

Thermally grown SiO2 layers on Si substrates implanted with Si+ ions with a dose of 6×1016cm−2 were studied by the techniques of photoluminescence, electron paramagnetic resonance (EPR), and low-frequency Raman scattering. Distinct oxygen-vacancy associated defects in SiO2 and non-bridging oxygen hole centers were identified by EPR. The luminescenc...