Taras Petrenko - Academia.edu (original) (raw)

Papers by Taras Petrenko

The Journal of Physical Chemistry A, 2002

A quantum chemical simulation for radicals of a cation branch in irradiated L-R-alanine crystals ... more A quantum chemical simulation for radicals of a cation branch in irradiated L-R-alanine crystals was carried out. The large cluster approach was used for investigation of possible paths of radical transformation. Both intermolecular and intramolecular proton transfer together with decarboxylation process were considered. Relative total energies of various radical structures were obtained at the PM3 level followed by DFT calculation of hyperfine parameters for the protons of the corresponding radical. It was shown that in this crystal the radicals R2 and R3 observed by ESR and ENDOR techniques are the products of the transformation of the primary cation radical.

Applied Surface Science, Dec 1, 2001

A brief review is given on EPR study of irradiation-induced defects in SiC. The results of low-te... more 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 C S symmetry, spin S ¼ 1 2 and close coincidence of the g-tensor components. For Ky2 defect the principal values of g-tensor have been determined as g z ¼ 2:0048, g x ¼ 2:0022 and g y ¼ 2:0037, where z and x directions reside in the ð1 1 2 0Þ plane and the z-axis makes up an angle 658 with the c-axis. The same residence of z-and xaxis and an angle 598 are found for Ky1 center, g z ¼ 2:0058, g x ¼ 2:0025 and g y ¼ 2:0023. A comparison of experimental and calculated hyperfine (HF) parameters is presented which suggests that Ky2 and Ky1 defects can be assigned to the positively charged carbon vacancy in 6H-SiC. The EPR study of defects created along the Al þ ion track in n-type 6H-SiC shows that lineshape, linewidth and integral intensity of the EPR signal reflect the state of damaged layer generated by ion implantation. A variation of defect density with annealing is reported and defect origin is discussed.

Interoperability and Architecture Requirements Analysis and Metadata Standardization for a Research Data Infrastructure in Catalysis

Communications in Computer and Information Science

A General Approach for Calculating Strongly Anharmonic Vibronic Spectra with a High Density of States: The X̃2B1 ← X̃1A1 Photoelectron Spectrum of Difluoromethane

Journal of Chemical Theory and Computation, 2017

Due to a low-lying fragmentation channel, the X̃(2)B1 ← X̃(1)A1 photoelectron spectrum of difluor... more Due to a low-lying fragmentation channel, the X̃(2)B1 ← X̃(1)A1 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 employing our recently developed residual-based algorithm for the calculation of eigenpairs (RACE). An analysis of the factors controlling the accuracy of the predicted band shape is provided. The calculated spectrum is in very close agreement with experimental results.

The Journal of chemical physics, Jan 28, 2017

Vibrational configuration interaction theory is a common method for calculating vibrational level... more 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 10(10) configurations. In general, this approach pursues the construction of the eigenstates with significant contributions of physically relevant configurations. The corresponding eigenfunctions are evaluated in the subspace of selected configurations. However, it can easily reach the dimension which is not tractable for conventional eigenvalue solvers. Although Davidson and Lanczos methods are the methods of choice for calculating exterior eigenvalues, they usually fall into stagnation when applied to interior states. The latter are commonly treated by the Jacobi-Davidson method. This approach in conjunction with matrix factorization for solving the correction equation (CE) is pro...

The Journal of Chemical Physics, 2015

The calculation of vibronic spectra and resonance Raman intensities can be performed on the basis... more 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 on the basis of the inhomogeneous Schrödinger equation using an iterative subspace method, in which explicit state-by-state calculations of vibrational eigenstates are bypassed. We study this approach within the framework of vibrational configuration interaction theory in conjunction with high-level electronic structure calculations for the multidimensional Born-Oppenheimer potential energy surface. The method benefits from an implicit account of interference effects between vibrational states, so that its computational cost correlates with the required resolution in the spectra. The accuracy and efficiency of the method with respect to co...

Advanced aspects of ab initio theoretical optical spectroscopy of transition metal complexes: Multiplets, spin-orbit coupling and resonance Raman intensities

Coordination Chemistry Reviews, 2007

In this review some advanced aspects of the theoretical methods for the calculation of transition... more 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 methods allow the correct zeroth order description of arbitrary electron

Journal of Molecular Structure: THEOCHEM, 2002

The molecular structures, harmonic frequencies, absolute infrared intensities and Raman scatterin... more The molecular structures, harmonic frequencies, absolute infrared intensities and Raman scattering activities have been calculated for metal triiodides, MI 3 (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 other ab initio calculations reported earlier. It is demonstrated that the density functional approach of Adamo and Barone, mPW1PW, [J. Chem. Phys. 108 (1990) 664] is superior to B3LYP and ab initio methods in predicting molecular structures and vibrational spectra of metal iodides.

Prediction of iron K-edge absorption spectra using time-dependent density functional theory

The journal of physical chemistry. A, Jan 18, 2008

Iron K-edge X-ray absorption pre-edge features have been calculated using a time-dependent densit... more 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, which span a range of high-spin and low-spin ferrous and ferric complexes in O(h) to T(d) geometries. Both quadrupole and dipole contributions to the spectra have been calculated. We find that good agreement between theory and experiment is obtained by using the BP86 functional with the CP(PPP) basis set on the Fe and TZVP one of the remaining atoms. Inclusion of solvation yields a small improvement in the calculated energies. However, the inclusion of scalar relativistic effects did not yield any improved correlation with experiment. The use of these methods to uniquely assign individual spectral transitions and to examine experimental c...

4.5 Challenges in Molecular Energy Research

Chemical Energy Storage, 2012

Structural transformations and silicon nanocrystallite formation in SiOx films

Semiconductors, 2001

Calculation of hyperfine parameters of positively charged carbon vacancy in SiC

Physica B: Condensed Matter, 2001

ABSTRACT Theoretical simulation of hyperfine parameters for the nearest and next-nearest neighbor... more ABSTRACT 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-functions. High performance of such approximations for the calculation of the hyperfine parameters of the well-known vacancy-related centers in SiC and Si has been demonstrated. We have found the D2d local symmetry for the VC+ in the SiC cubic cluster. In hexagonal-like cluster, the D2d symmetry is lowered to the CS one. The symmetry plane contains the c-axis and one of the transverse bonds. Four Si atoms of the first shell become essentially inequivalent and have different hyperfine parameters. Two in-plane Si atoms concentrate the major part of the spin density and out-of-plane Si atoms exhibit relatively small hyperfine parameters.

The carbon 100 split interstitial in SiC

Journal of Physics: Condensed Matter, 2002

Photoluminescence and paramagnetic defects in silicon-implanted silicon dioxide layers

Journal of Luminescence, 1998

Thermally grown SiO2 layers on Si substrates implanted with Si+ ions with a dose of 6×1016cm−2 we... more 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 luminescence intensity in the 620nm range was found to correlate with the number of these defects. The low-frequency Raman scattering technique was used to estimate the average size of the Si nanocrystallites formed after the implantation and thermal annealing at T>1100°C, which are responsible for the photoluminescence band with a maximum at 740nm. The intensity of this band can be significantly enhanced by an additional treatment of the samples in a low-temperature RF plasma.

Efficient time-dependent density functional theory approximations for hybrid density functionals: Analytical gradients and parallelization

The Journal of Chemical Physics, 2011

In this paper, we present the implementation of efficient approximations to time-dependent densit... more 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 computation of the Coulomb terms and the recently introduced “chain of spheres exchange” (COSX) algorithm for the calculation of the exchange terms. It is shown that for extended basis sets, the RIJCOSX approximation leads to speedups of up to 2 orders of magnitude compared to traditional methods, as demonstrated for hydrocarbon chains. The accuracy of the adiabatic transition energies, excited state structures, and vibrational frequencies is assessed on a set of 27 excited states for 25 molecules with the configuration interaction singles and hybrid TDDFT/TDA methods using various basis sets. Compared to the canonical values, the typical err...

Efficient and automatic calculation of optical band shapes and resonance Raman spectra for larger molecules within the independent mode displaced harmonic oscillator model

The Journal of Chemical Physics, 2012

In this work, an improved method for the efficient automatic simulation of optical band shapes an... more 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 spectra corresponding to strongly dipole allowed electronic transitions with high accuracy. In order to include temperature-induced effects, we propose a simple extension of the time dependent wavepacket formalism developed by Heller which enables one to derive analytical expressions for the intensities of hot bands in ABS and rR spectra from the dependence of the wavepacket evolution on its initial coordinate. We have also greatly optimized the computational procedures for numerical integration of complicated oscillating integrals. This is important for efficient simulations of higher-order rR spectra and excitation profiles, as well as for...

Magnetic and Spectroscopic Properties of Mixed Valence Manganese(III,IV) Dimers: A Systematic Study Using Broken Symmetry Density Functional Theory

Inorganic Chemistry, 2009

Exchange coupling parameters and isotropic (55)Mn hyperfine couplings of fourteen mixed-valence M... more 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 constants among all investigated methods, with deviations from experiment of the order of approximately 10-15%. For the prediction of (55)Mn hyperfine couplings the deficiencies of DFT in the description of core-level spin-polarization and the neglect of scalar relativistic effects lead to systematic deviations between theory and experiment that can be compensated through the use of a universal scaling factor. We determine this scaling factor to be 1.49 and demonstrate that the (55)Mn hyperfine couplings in mixed-valence Mn(III,IV) dimers can be successfully and systematically predicted with the TPSSh functional and the proposed spin projection techniques. The dependence of isotropic (55)Mn hyperfine couplings on the Mn(III) zero-field splitting values is studied in detail using a dimer for which the strong exchange approximation breaks down. In this case we apply a rigorous form of our spin projection technique that incorporates zero-field splitting contributions to the site spin expectation values. These results form the basis for future studies that aim at deducing unknown structures on the basis of computed spectroscopic parameters.

Symmetry, spin state and hyperfine parameters of vacancies in cubic SiC

Applied Surface Science, 2001

ABSTRACT Cluster calculation of carbon and silicon vacancies in cubic SiC has been performed for ... more ABSTRACT 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 calculations of hyperfine coupling parameters for atoms of the first and second shells of vacancies have been performed. The test calculations have been done to check the validity of applied approximations, and reasonable agreement between calculated and experimental data has been obtained. The ground spin state and the defect point symmetry for all the above-mentioned charge states have been determined along with the hyperfine parameters for atoms of the first and second shells. In the ground state, spins of VC−, VSi− and VSi+ have the value of , while S=1 for VC0 and VSi0, and for VC+. Optimization of geometry leads to a minimum with the Td symmetry only for VC−, VSi− and VSi+ centers. At the same time, VSi0 and VC+ defects have D2d symmetry, while VC0 has C3V symmetry. All the considered charge states of the carbon vacancy exhibit remarkably stronger hyperfine interaction with the nearest and next-nearest neighbors as compared to the silicon vacancy.

A negatively charged silicon vacancy in SiC: Spin polarization effects

Physics of the Solid State, 2002

ABSTRACT The equilibrium geometry and hyperfine interaction constants of the nearest and next-to-... more ABSTRACT 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 calculations with the use of a 70-atom cluster are in good agreement with experimental data. A detailed consideration is given to spin polarization in the electron subsystem and the applicability of a simple LCAO model that is commonly used in the interpretation of the electron paramagnetic resonance data for semiconductors. The spin density distribution for the defect under investigation is analyzed in terms of localized orbitals.

EPR Study of the Mn-Doped Magnesium Titanate Ceramics

ECS Journal of Solid State Science and Technology, 2022

Manganese-doped magnesium titanate ceramic samples obtained by a solid-state reaction via sinteri... more Manganese-doped magnesium titanate ceramic samples obtained by a solid-state reaction via sintering in the air from a mixture of MgO and TiO2 powders of different molar ratios were analyzed by electron paramagnetic resonance (EPR) technique. The EPR signals of Mn2+ ions (S = 5/2, І = 5/2) in crystal phases of MgO, Mg2TiO4, and MgTiO3 were detected. We have obtained the following spin Hamiltonian parameters for Mn2+ ions: g = 2.0015, A ~ 81 ∗ 10-4 cm-1 (in MgO phase); g = 2.0029, A ~ 73.8 ∗ 10-4 cm-1, b2 0 = 35 ∗ 10-4 cm-1 (in Mg2TiO4 phase); g = 2.004, A ~ 79 ∗ 10-4 cm-1, b2 0 = 165 ∗ 10-4 cm-1 (in MgTiO3 phase). Despite the presence of Mn4+ centers in both Mg2TiO4:Mn and MgTiO3:Mn ceramics confirmed by previous optical studies, no EPR signals related to Mn4+ ions (S = 3/2, І = 5/2) were found. The Mn2+ EPR signals are proposed as structural probes in manganese-doped magnesium titanate ceramics.