Elena Sheka - Profile on Academia.edu (original) (raw)
Papers by Elena Sheka
Carbon materials, 2013
Discussed in the paper is aimed at convincing readers that sp 2 nanocarbons present a new class o... more Discussed in the paper is aimed at convincing readers that sp 2 nanocarbons present a new class of topochemical objects. The novelty lies in the fact that these species demonstrate a complicated topological behavior in regards chemical reactions with their participation that manifest a combination of the inherent topology of the species, or the internal topology, with that provided by the action of external factors. The internal topology is manifested through identical reactions that involve different members of the class. Two types of such reactions have been considered, namely, the 'double-(C-C)bond' reactions between two sp 2 -class members and 'atom-(C-C)-bond' reactions that concern a low-atomic species deposition on the nanocarbons. The former reaction is mainly addressed to a number of composites that are formed by fullerene C 60 attachment to either itself, or carbon nanotube and nanographene. As turned out, in spite of structural similarity of the 'double-(C-C)-bond' contact zones, which are mainly presented by [2+2] cycloaddition junctions, the energetic parameters of the composites have revealed a deep discrepancy that manifest the different inherent topology of the species [1]. This conclusion finds support in case of composites formed by carbon nanotubes and graphene, as well . But the brightest proof of the difference in the inherent topology of fullerenes and graphene has been obtained by comparing the hydrogenation and oxidation of fullerene C 60 and (5, 5) nanographene . The external topological events have been demonstrated computationally by different both structural image and energetic characteristics of (5, 5) nanographene hydrides and oxides under conditions when the pristine graphene membrane was subjected to the action of different external factors, such as: immobilization of the periphery carbon atoms, restrictions of the accessibility of both sides of the membrane, and exploring either atomic and molecular hydrogen or oxygen molecule, hydroxyl, and carboxyl units. This finding seems to be of particular importance since it should be addressed to the chemical modification of graphene as a methodology aimed at a controllable changing of the graphene electronic properties. It is quite obvious that chemical behavior of graphene in the form of free-standing and fixed membranes, deposited layers on different substrates, in solutions and gaseous surroundings will be different. The analysis of the available experimental data gave a large support of the conclusion.
Progress in theoretical chemistry and physics, 2013
In view of a formal topology, two common terms, namely, connectivity and adjacency, determine the... more In view of a formal topology, two common terms, namely, connectivity and adjacency, determine the 'quality' of C-C bonds of sp 2 nanocarbons. The feature is the most sensitive point of the inherent topology of the species so that such external action as mechanical deformation should obviously change it and result in particular topological effects. The current paper describes the effects caused by uniaxial tension of a graphene molecule in due course of a mechanochemical reaction. Basing on the molecular theory of graphene, the effects are attributed to both mechanical loading and chemical modification of edge atoms of the molecule. The mechanical behavior is shown to be not only highly anisotropic with respect to the direction of the load application, but greatly dependent on the chemical modification of the molecule edge atoms thus revealing topological character of the graphene deformation.
Fullerene nanoclusters as enhancers in linear spectroscopy and nonlinear optics
High Energy Chemistry, Dec 1, 2009
ABSTRACT The enhancement of nonlinear optical phenomena in fullerene solutions is treated in term... more ABSTRACT The enhancement of nonlinear optical phenomena in fullerene solutions is treated in terms of the model of amplification of local electric field due to resonance excitation of clusters, which are extended chargetransfer complexes. Excitation light is transformed in the clusters into local charge-transfer excitons, inducing polarization of the medium sufficient for amplification of the local electric field of incident and exiting light. The intensity of the observed linear optical phenomena has been directly correlated with the magnitude of the nonlinear characteristics of the medium on one hand and the efficiency of clustering on the other hand. The gain coefficients have been determined. Experimental and computational testing procedures that make it possible to determine suitability of the fullerene-doped matrix for nonlinear-optics applications are proposed.
Journal of Experimental and Theoretical Physics, May 1, 2014
Photoluminescence of graphene quantum dots (GQDs) of shungite, attributed to individual fragments... more Photoluminescence of graphene quantum dots (GQDs) of shungite, attributed to individual fragments of reduced graphene oxide (rGO), has been studied for the frozen rGO colloidal dispersions in water, carbon tetrachloride, and toluene. Morphological study shows a steady trend of GQDs to form fractals and a drastic change in the colloids fractal structure caused by solvent was reliably established. Spectral study reveals a dual character of emitting centers: individual GQDs are responsible for the spectra position while fractal structure of GQD colloids provides high broadening of the spectra due to structural inhomogeneity of the colloidal dispersions and a peculiar dependence on excitation wavelength. For the first time, photoluminescence spectra of individual GQDs were observed in frozen toluene dispersions which pave the way for a theoretical treatment of GQD photonics.
Journal of Materials Chemistry, 2011
The current paper presents the third part of the study devoted to composites formed by fullerene ... more The current paper presents the third part of the study devoted to composites formed by fullerene C 60 and two graphene nanosheets ([C 60 +(5,5)] and ([C 60 +(9, 8)] graphene nanobuds). The formation of composites is considered from the basic points related to the atomic chemical reactivity of the fullerene molecule and nanographene. The barrier that governs the composites formation is determined in terms of the coupling energy tot cpl E and is expanded over two contributions that present the total energy of deformation of the composites' components tot def E and the energy of covalent coupling tot E cov . In view of these energetic parameters and in contrast to expectations, seemingly identical reactions that are responsible for the formation of intermolecular contacts in (C 60 ) 2 dimer, [C 60 +(4,4)] carbon nanobuds, and [C 60 +(5,5)] and [C 60 +(9,8)] graphene nanobuds result in different final products. The peculiarity is suggested to result from a topochemical character of the covalent coupling between two members of the sp 2 nanocarbons' family. The computations were performed by using the AM1 semiempirical version of unrestricted broken symmetry Hartree-Fock approach.
The paper presents a quantum-chemical approach to two aspects of fullerene nanomedicine related t... more The paper presents a quantum-chemical approach to two aspects of fullerene nanomedicine related to the oxidative and antioxidant actions of fullerene. The first topic is concerned in regards photodynamic therapeutic effect of fullerene solutions. A new mechanism of the effect is proposed. The second aspect is exemplified by the consideration of two fullerene-silica complexes, namely, fullerosil and fullerosilica gel. Статья посвящается памяти талантливого ученого, креативного лидера и большого человека, любившего науку и считавшего ее делом своей жизни, умевшего одинаково искренне радоваться своим и чужим успехам, Алексея Алексеевича Чуйко. Автору дороги все встречи и беседы с этим неординарным человеком, стимулировавшие, в частности, и это исследование.
The nature of enhanced linear and nonlinear optical effects in fullerene solutions
Journal of Experimental and Theoretical Physics, May 1, 2009
The “blue” emission from fullerene C60 and its derivatives in frozen toluene solution is discover... more The “blue” emission from fullerene C60 and its derivatives in frozen toluene solution is discovered and analyzed in the framework of the electromagnetic theory of enhanced optical effects. It is shown that the emission, combining enhanced spectra of Raman scattering and one-photon luminescence, is due to clustering of fullerene molecules in solution. Photoexcitation of charge-transfer excitons in clusters provides the polarization required for the enhancement. A direct relationship is established between the observed phenomenon and nonlinear optical properties of the medium. Empirical and computational tests are proposed to select matrices with various nonlinear optical properties.
Progress in theoretical chemistry and physics, 2013
Odd electrons of benzenoid units and correlation of these electrons having different spins are th... more Odd electrons of benzenoid units and correlation of these electrons having different spins are the main concepts of the molecular theory of graphene. In contrast to the theory of aromaticity, the molecular theory is based on the fact that odd electrons with different spins occupy different places in the space so that the configuration interaction becomes the central point of the theory. Consequently, a multi-determinant presentation of the wave function of the system of weakly interacting odd electrons is absolutely mandatory on the way of the theory realization at the computational level. However, the efficacy of the available CI computational techniques is quite restricted in regards large polyatomic systems, which does not allow performing extensive computational experiments. Facing the problem, computationists have addressed to standard single-determinant ones albeit not often being aware of how correct are the obtained results. The current chapter presents the molecular theory of graphene in terms of single-determinant computational schemes and discloses how reliable information about electron-correlated system can be obtained by using either UHF or UDFT computational schemes. When the paper was written, a beautiful conceptually profound 'informal reflection' of Roald Hoffmann appeared in the first issue of the Angewandte Chemie (International Eddition) that celebrates its 125-year anniversary [1]. Hoffmann's "Small but Strong Lessons from Chemistry for Nanoscience" turned out to be remarkably concordant to the main ideas discussed in the current paper. This should be expected since the Hofmann concepts on stabilizing singlet states of biradicals in organic chemistry (see [2] and references therein) and dimeric molecular magnets have led the foundation of the molecular theory of fullerenes , application of which to graphene science is discussed below. These problems are on knife-edge today that is why, once fully agree with Hoffmann's answers to the question 'What you can trust about theory?', I would like to preface the presentation of the text of a quote from the 'informal reflection', placing it as the epigraph It goes without saying that theory is really of value when it is used to perform numerical experiments that capture a trend. Not numbers, but a trend.
Spin Effects in sp 2 Nanocarbons in the Light of Unrestricted Hartree-Fock Approach and Spin-Orbit Coupling Theory
Progress in theoretical chemistry and physics, 2017
The paper presents the first reference to the post factum similarity of nonrelativistic unrestric... more The paper presents the first reference to the post factum similarity of nonrelativistic unrestricted Hartree-Fock formalism and Dirac-Fock spin-orbit theory when applying for the consideration of spin effects characteristic for sp 2 nanocarbon open-shell molecules (fullerenes, carbon nanotubes, and graphene). The origin of the similarity as well as interchangeability of the approaches when determining either UHF or SOC peculiarities and parameters are discussed.
Наносистемы: физика, химия, математика, Dec 21, 2016
The paper presents a comparative consideration of sp 2 nanocarbons and their silicon and higher t... more The paper presents a comparative consideration of sp 2 nanocarbons and their silicon and higher tetrels analogues from the viewpoint of the spin molecular theory taking into account the electron correlation in open-shell molecules. High radicalization of silicene and quantum instability of flat honeycomb 2D structures of germanene and stanene make all the species phantom materials leaving graphene the only one-atom thick 2D solid free of the crucial restrictions.
Наносистемы: физика, химия, математика, Feb 24, 2016
The current paper presents results from an extended neutron scattering study of a three-part set ... more The current paper presents results from an extended neutron scattering study of a three-part set of parent and reduced graphene oxides (GO and rGO, respectively) of different origins. The first part concerns the rGO of natural origin represented by shungite carbon, the second and third parts are related to synthetic GO/rGO pairs with the latter produced during either chemical treatment or via thermal exfoliation of the parent GO, respectively. The study involved both the neutron diffraction and inelastic neutron scattering. The one-phonon amplitude-weighted density of vibrational states G(ω) represents the inelastic incoherent neutron scattering spectra of the products. Common characteristics and individual distinctions of the studied species are discussed.
Journal of Experimental and Theoretical Physics, Sep 1, 2010
The reactions of fullerene C 60 with atomic fluorine have been studied by unrestricted broken spi... more The reactions of fullerene C 60 with atomic fluorine have been studied by unrestricted broken spin-symmetry Hartree-Fock (UBS HF) approach implemented in semiempirical codes based on AM1 technique. The calculations were focused on a sequential addition of fluorine atom to the fullerene cage following indication of the cage atom highest chemical susceptibility that is calculated at each step. The effectively-non-paired-electron concept of the fullerene atoms chemical susceptibility lays the foundation of the suggested computational synthesis. The obtained results are analyzed from energetic, symmetry, and the composition abundance viewpoints. A good fitting of the data to experimental findings proves a creative role of the suggested synthesis methodology.
Polymers
The first case of virtual polymerization based on the concept of digital twins (DTs) is presented... more The first case of virtual polymerization based on the concept of digital twins (DTs) is presented. The free-radical polymerization of vinyl monomers is considered to be a chain reaction consisting of a set of elementary ones. Those three types, related to the polymerization initiation and propagation as well as to the termination of polymer chain growth, are discussed. Special sets of DTs, whose total number approaches 60, distinguish each reaction type. The calculations are carried out using a semi-empirical version of the unrestricted Hartree–Fock approximation. The main energy and spin-density parameters of the ground state of the DTs are determined. The barrier profiles of two pairs of DTs are calculated, based on which two Evans–Polanyi–Semenov relations, attributed to elementary reactions of type (1) and (2), are constructed. These provide a quite reliable evaluation of the activation energy for the initiation and propagation of the free-radical polymerization of vinyl monomer...
In the imagination of the majority of quantum computationists, involved in the graphene nanoscien... more In the imagination of the majority of quantum computationists, involved in the graphene nanoscience, the motion of weakly bound odd electrons of graphene with different spins is not correlated. Only this fact can justify them using computational techniques based on single restricted closed-shell determinants such as widely used DFT schemes. Sometimes, the schemes have even been heralded as indisputable standard of the computations in the field. However, the electron behavior in graphene is much richer and does not fit a Procrustean bed of the electron correlation neglect just revealing peculiariries related to graphene edges, structurally inhomogeneous chemical reactivity, size-dependent magnetism, enhancement of the electron density of graphene bubles, and so forth.
physica status solidi (b), 1972
We present an extremely simple formulation of inelastic incoherent neutron scattering from impure... more We present an extremely simple formulation of inelastic incoherent neutron scattering from impure crystals. The formulation treats both mass and central‐force‐constant changes at the defect site in a closed form which is immediately amenable to an experimental analysis.
Journal of Luminescence, 1994
Heat-pulse and time-resolved luminescence experiments are performed on bound excitons in dilute G... more Heat-pulse and time-resolved luminescence experiments are performed on bound excitons in dilute GaP: N. The V band is shown to arise from both zero-phonon and phonon-assisted recombination of excitons from the B state. The shape of the V band is determined by the Bohr radius of the exciton. From the time-resolved luminescence experiments, we derive a time of 300 ns for exciton energy transfer to disturbed sites.
arXiv (Cornell University), Jul 12, 2022
A still amazing identity of the D-G doublet Raman spectra of parental and reduced graphene oxides... more A still amazing identity of the D-G doublet Raman spectra of parental and reduced graphene oxides is considered from the digital twins' viewpoint. About thirty DTs, presenting different aspects of the GO structure and properties, were virtually synthesized using atomic spin-density algorithm, which allowed reliably displaying reasons for this extraordinary spectral feature. In both cases, it was established that the D-G doublets owe their origin to the sp 3 -sp 2 C-C stretchings, respectively. This outwardly similar community of the doublets' origin of GO and rGO is thoroughly analyzed to reveal different grounds of the feature in the two cases. Multilayer packing of individual rGO molecules in stacks, in the first case, and spin-influenced prohibition of the 100% oxidative reaction, the termination of which is accompanied with a particular set of highly ordered by length sp 3 -and sp 2 C-C bonds, protecting the carbon carcass from destruction caused by the stress induced sp 2 -to-sp 3 transformation, in the second, are the main reasons. The DT concept has been realized on the basis of virtual vibrational spectrometer HF Spectrodyn.
Neutron Scattering from Equilibrium and Non-equilibrium Phonons, Excitons and Polaritons
Molecular Crystals and Liquid Crystals
Surface magnetism of silicon [111](7/spl times/7) and [001](2/spl times/1) surfaces: quantum-chemical approach
1999 9th International Crimean Microwave Conference 'Microwave and Telecommunication Technology'. Conference Proceedings (IEEE Cat. No.99EX363), 1999
ABSTRACT When discussing bare surfaces of silicon crystal, the concept of dangling bonds is widel... more ABSTRACT When discussing bare surfaces of silicon crystal, the concept of dangling bonds is widely used. The surface reconstruction is usually explained in terms of a tendency of the bonds to be saturated. However, the current microscopic calculations show that the availability of dangling bonds on the topmost silicon atoms is controversial enough
Davydov Splitting in the Absorption Spectra of Molecular Crystals
Molecular Crystals and Liquid Crystals, 1975
ABSTRACT
Carbon materials, 2013
Discussed in the paper is aimed at convincing readers that sp 2 nanocarbons present a new class o... more Discussed in the paper is aimed at convincing readers that sp 2 nanocarbons present a new class of topochemical objects. The novelty lies in the fact that these species demonstrate a complicated topological behavior in regards chemical reactions with their participation that manifest a combination of the inherent topology of the species, or the internal topology, with that provided by the action of external factors. The internal topology is manifested through identical reactions that involve different members of the class. Two types of such reactions have been considered, namely, the 'double-(C-C)bond' reactions between two sp 2 -class members and 'atom-(C-C)-bond' reactions that concern a low-atomic species deposition on the nanocarbons. The former reaction is mainly addressed to a number of composites that are formed by fullerene C 60 attachment to either itself, or carbon nanotube and nanographene. As turned out, in spite of structural similarity of the 'double-(C-C)-bond' contact zones, which are mainly presented by [2+2] cycloaddition junctions, the energetic parameters of the composites have revealed a deep discrepancy that manifest the different inherent topology of the species [1]. This conclusion finds support in case of composites formed by carbon nanotubes and graphene, as well . But the brightest proof of the difference in the inherent topology of fullerenes and graphene has been obtained by comparing the hydrogenation and oxidation of fullerene C 60 and (5, 5) nanographene . The external topological events have been demonstrated computationally by different both structural image and energetic characteristics of (5, 5) nanographene hydrides and oxides under conditions when the pristine graphene membrane was subjected to the action of different external factors, such as: immobilization of the periphery carbon atoms, restrictions of the accessibility of both sides of the membrane, and exploring either atomic and molecular hydrogen or oxygen molecule, hydroxyl, and carboxyl units. This finding seems to be of particular importance since it should be addressed to the chemical modification of graphene as a methodology aimed at a controllable changing of the graphene electronic properties. It is quite obvious that chemical behavior of graphene in the form of free-standing and fixed membranes, deposited layers on different substrates, in solutions and gaseous surroundings will be different. The analysis of the available experimental data gave a large support of the conclusion.
Progress in theoretical chemistry and physics, 2013
In view of a formal topology, two common terms, namely, connectivity and adjacency, determine the... more In view of a formal topology, two common terms, namely, connectivity and adjacency, determine the 'quality' of C-C bonds of sp 2 nanocarbons. The feature is the most sensitive point of the inherent topology of the species so that such external action as mechanical deformation should obviously change it and result in particular topological effects. The current paper describes the effects caused by uniaxial tension of a graphene molecule in due course of a mechanochemical reaction. Basing on the molecular theory of graphene, the effects are attributed to both mechanical loading and chemical modification of edge atoms of the molecule. The mechanical behavior is shown to be not only highly anisotropic with respect to the direction of the load application, but greatly dependent on the chemical modification of the molecule edge atoms thus revealing topological character of the graphene deformation.
Fullerene nanoclusters as enhancers in linear spectroscopy and nonlinear optics
High Energy Chemistry, Dec 1, 2009
ABSTRACT The enhancement of nonlinear optical phenomena in fullerene solutions is treated in term... more ABSTRACT The enhancement of nonlinear optical phenomena in fullerene solutions is treated in terms of the model of amplification of local electric field due to resonance excitation of clusters, which are extended chargetransfer complexes. Excitation light is transformed in the clusters into local charge-transfer excitons, inducing polarization of the medium sufficient for amplification of the local electric field of incident and exiting light. The intensity of the observed linear optical phenomena has been directly correlated with the magnitude of the nonlinear characteristics of the medium on one hand and the efficiency of clustering on the other hand. The gain coefficients have been determined. Experimental and computational testing procedures that make it possible to determine suitability of the fullerene-doped matrix for nonlinear-optics applications are proposed.
Journal of Experimental and Theoretical Physics, May 1, 2014
Photoluminescence of graphene quantum dots (GQDs) of shungite, attributed to individual fragments... more Photoluminescence of graphene quantum dots (GQDs) of shungite, attributed to individual fragments of reduced graphene oxide (rGO), has been studied for the frozen rGO colloidal dispersions in water, carbon tetrachloride, and toluene. Morphological study shows a steady trend of GQDs to form fractals and a drastic change in the colloids fractal structure caused by solvent was reliably established. Spectral study reveals a dual character of emitting centers: individual GQDs are responsible for the spectra position while fractal structure of GQD colloids provides high broadening of the spectra due to structural inhomogeneity of the colloidal dispersions and a peculiar dependence on excitation wavelength. For the first time, photoluminescence spectra of individual GQDs were observed in frozen toluene dispersions which pave the way for a theoretical treatment of GQD photonics.
Journal of Materials Chemistry, 2011
The current paper presents the third part of the study devoted to composites formed by fullerene ... more The current paper presents the third part of the study devoted to composites formed by fullerene C 60 and two graphene nanosheets ([C 60 +(5,5)] and ([C 60 +(9, 8)] graphene nanobuds). The formation of composites is considered from the basic points related to the atomic chemical reactivity of the fullerene molecule and nanographene. The barrier that governs the composites formation is determined in terms of the coupling energy tot cpl E and is expanded over two contributions that present the total energy of deformation of the composites' components tot def E and the energy of covalent coupling tot E cov . In view of these energetic parameters and in contrast to expectations, seemingly identical reactions that are responsible for the formation of intermolecular contacts in (C 60 ) 2 dimer, [C 60 +(4,4)] carbon nanobuds, and [C 60 +(5,5)] and [C 60 +(9,8)] graphene nanobuds result in different final products. The peculiarity is suggested to result from a topochemical character of the covalent coupling between two members of the sp 2 nanocarbons' family. The computations were performed by using the AM1 semiempirical version of unrestricted broken symmetry Hartree-Fock approach.
The paper presents a quantum-chemical approach to two aspects of fullerene nanomedicine related t... more The paper presents a quantum-chemical approach to two aspects of fullerene nanomedicine related to the oxidative and antioxidant actions of fullerene. The first topic is concerned in regards photodynamic therapeutic effect of fullerene solutions. A new mechanism of the effect is proposed. The second aspect is exemplified by the consideration of two fullerene-silica complexes, namely, fullerosil and fullerosilica gel. Статья посвящается памяти талантливого ученого, креативного лидера и большого человека, любившего науку и считавшего ее делом своей жизни, умевшего одинаково искренне радоваться своим и чужим успехам, Алексея Алексеевича Чуйко. Автору дороги все встречи и беседы с этим неординарным человеком, стимулировавшие, в частности, и это исследование.
The nature of enhanced linear and nonlinear optical effects in fullerene solutions
Journal of Experimental and Theoretical Physics, May 1, 2009
The “blue” emission from fullerene C60 and its derivatives in frozen toluene solution is discover... more The “blue” emission from fullerene C60 and its derivatives in frozen toluene solution is discovered and analyzed in the framework of the electromagnetic theory of enhanced optical effects. It is shown that the emission, combining enhanced spectra of Raman scattering and one-photon luminescence, is due to clustering of fullerene molecules in solution. Photoexcitation of charge-transfer excitons in clusters provides the polarization required for the enhancement. A direct relationship is established between the observed phenomenon and nonlinear optical properties of the medium. Empirical and computational tests are proposed to select matrices with various nonlinear optical properties.
Progress in theoretical chemistry and physics, 2013
Odd electrons of benzenoid units and correlation of these electrons having different spins are th... more Odd electrons of benzenoid units and correlation of these electrons having different spins are the main concepts of the molecular theory of graphene. In contrast to the theory of aromaticity, the molecular theory is based on the fact that odd electrons with different spins occupy different places in the space so that the configuration interaction becomes the central point of the theory. Consequently, a multi-determinant presentation of the wave function of the system of weakly interacting odd electrons is absolutely mandatory on the way of the theory realization at the computational level. However, the efficacy of the available CI computational techniques is quite restricted in regards large polyatomic systems, which does not allow performing extensive computational experiments. Facing the problem, computationists have addressed to standard single-determinant ones albeit not often being aware of how correct are the obtained results. The current chapter presents the molecular theory of graphene in terms of single-determinant computational schemes and discloses how reliable information about electron-correlated system can be obtained by using either UHF or UDFT computational schemes. When the paper was written, a beautiful conceptually profound 'informal reflection' of Roald Hoffmann appeared in the first issue of the Angewandte Chemie (International Eddition) that celebrates its 125-year anniversary [1]. Hoffmann's "Small but Strong Lessons from Chemistry for Nanoscience" turned out to be remarkably concordant to the main ideas discussed in the current paper. This should be expected since the Hofmann concepts on stabilizing singlet states of biradicals in organic chemistry (see [2] and references therein) and dimeric molecular magnets have led the foundation of the molecular theory of fullerenes , application of which to graphene science is discussed below. These problems are on knife-edge today that is why, once fully agree with Hoffmann's answers to the question 'What you can trust about theory?', I would like to preface the presentation of the text of a quote from the 'informal reflection', placing it as the epigraph It goes without saying that theory is really of value when it is used to perform numerical experiments that capture a trend. Not numbers, but a trend.
Spin Effects in sp 2 Nanocarbons in the Light of Unrestricted Hartree-Fock Approach and Spin-Orbit Coupling Theory
Progress in theoretical chemistry and physics, 2017
The paper presents the first reference to the post factum similarity of nonrelativistic unrestric... more The paper presents the first reference to the post factum similarity of nonrelativistic unrestricted Hartree-Fock formalism and Dirac-Fock spin-orbit theory when applying for the consideration of spin effects characteristic for sp 2 nanocarbon open-shell molecules (fullerenes, carbon nanotubes, and graphene). The origin of the similarity as well as interchangeability of the approaches when determining either UHF or SOC peculiarities and parameters are discussed.
Наносистемы: физика, химия, математика, Dec 21, 2016
The paper presents a comparative consideration of sp 2 nanocarbons and their silicon and higher t... more The paper presents a comparative consideration of sp 2 nanocarbons and their silicon and higher tetrels analogues from the viewpoint of the spin molecular theory taking into account the electron correlation in open-shell molecules. High radicalization of silicene and quantum instability of flat honeycomb 2D structures of germanene and stanene make all the species phantom materials leaving graphene the only one-atom thick 2D solid free of the crucial restrictions.
Наносистемы: физика, химия, математика, Feb 24, 2016
The current paper presents results from an extended neutron scattering study of a three-part set ... more The current paper presents results from an extended neutron scattering study of a three-part set of parent and reduced graphene oxides (GO and rGO, respectively) of different origins. The first part concerns the rGO of natural origin represented by shungite carbon, the second and third parts are related to synthetic GO/rGO pairs with the latter produced during either chemical treatment or via thermal exfoliation of the parent GO, respectively. The study involved both the neutron diffraction and inelastic neutron scattering. The one-phonon amplitude-weighted density of vibrational states G(ω) represents the inelastic incoherent neutron scattering spectra of the products. Common characteristics and individual distinctions of the studied species are discussed.
Journal of Experimental and Theoretical Physics, Sep 1, 2010
The reactions of fullerene C 60 with atomic fluorine have been studied by unrestricted broken spi... more The reactions of fullerene C 60 with atomic fluorine have been studied by unrestricted broken spin-symmetry Hartree-Fock (UBS HF) approach implemented in semiempirical codes based on AM1 technique. The calculations were focused on a sequential addition of fluorine atom to the fullerene cage following indication of the cage atom highest chemical susceptibility that is calculated at each step. The effectively-non-paired-electron concept of the fullerene atoms chemical susceptibility lays the foundation of the suggested computational synthesis. The obtained results are analyzed from energetic, symmetry, and the composition abundance viewpoints. A good fitting of the data to experimental findings proves a creative role of the suggested synthesis methodology.
Polymers
The first case of virtual polymerization based on the concept of digital twins (DTs) is presented... more The first case of virtual polymerization based on the concept of digital twins (DTs) is presented. The free-radical polymerization of vinyl monomers is considered to be a chain reaction consisting of a set of elementary ones. Those three types, related to the polymerization initiation and propagation as well as to the termination of polymer chain growth, are discussed. Special sets of DTs, whose total number approaches 60, distinguish each reaction type. The calculations are carried out using a semi-empirical version of the unrestricted Hartree–Fock approximation. The main energy and spin-density parameters of the ground state of the DTs are determined. The barrier profiles of two pairs of DTs are calculated, based on which two Evans–Polanyi–Semenov relations, attributed to elementary reactions of type (1) and (2), are constructed. These provide a quite reliable evaluation of the activation energy for the initiation and propagation of the free-radical polymerization of vinyl monomer...
In the imagination of the majority of quantum computationists, involved in the graphene nanoscien... more In the imagination of the majority of quantum computationists, involved in the graphene nanoscience, the motion of weakly bound odd electrons of graphene with different spins is not correlated. Only this fact can justify them using computational techniques based on single restricted closed-shell determinants such as widely used DFT schemes. Sometimes, the schemes have even been heralded as indisputable standard of the computations in the field. However, the electron behavior in graphene is much richer and does not fit a Procrustean bed of the electron correlation neglect just revealing peculiariries related to graphene edges, structurally inhomogeneous chemical reactivity, size-dependent magnetism, enhancement of the electron density of graphene bubles, and so forth.
physica status solidi (b), 1972
We present an extremely simple formulation of inelastic incoherent neutron scattering from impure... more We present an extremely simple formulation of inelastic incoherent neutron scattering from impure crystals. The formulation treats both mass and central‐force‐constant changes at the defect site in a closed form which is immediately amenable to an experimental analysis.
Journal of Luminescence, 1994
Heat-pulse and time-resolved luminescence experiments are performed on bound excitons in dilute G... more Heat-pulse and time-resolved luminescence experiments are performed on bound excitons in dilute GaP: N. The V band is shown to arise from both zero-phonon and phonon-assisted recombination of excitons from the B state. The shape of the V band is determined by the Bohr radius of the exciton. From the time-resolved luminescence experiments, we derive a time of 300 ns for exciton energy transfer to disturbed sites.
arXiv (Cornell University), Jul 12, 2022
A still amazing identity of the D-G doublet Raman spectra of parental and reduced graphene oxides... more A still amazing identity of the D-G doublet Raman spectra of parental and reduced graphene oxides is considered from the digital twins' viewpoint. About thirty DTs, presenting different aspects of the GO structure and properties, were virtually synthesized using atomic spin-density algorithm, which allowed reliably displaying reasons for this extraordinary spectral feature. In both cases, it was established that the D-G doublets owe their origin to the sp 3 -sp 2 C-C stretchings, respectively. This outwardly similar community of the doublets' origin of GO and rGO is thoroughly analyzed to reveal different grounds of the feature in the two cases. Multilayer packing of individual rGO molecules in stacks, in the first case, and spin-influenced prohibition of the 100% oxidative reaction, the termination of which is accompanied with a particular set of highly ordered by length sp 3 -and sp 2 C-C bonds, protecting the carbon carcass from destruction caused by the stress induced sp 2 -to-sp 3 transformation, in the second, are the main reasons. The DT concept has been realized on the basis of virtual vibrational spectrometer HF Spectrodyn.
Neutron Scattering from Equilibrium and Non-equilibrium Phonons, Excitons and Polaritons
Molecular Crystals and Liquid Crystals
Surface magnetism of silicon [111](7/spl times/7) and [001](2/spl times/1) surfaces: quantum-chemical approach
1999 9th International Crimean Microwave Conference 'Microwave and Telecommunication Technology'. Conference Proceedings (IEEE Cat. No.99EX363), 1999
ABSTRACT When discussing bare surfaces of silicon crystal, the concept of dangling bonds is widel... more ABSTRACT When discussing bare surfaces of silicon crystal, the concept of dangling bonds is widely used. The surface reconstruction is usually explained in terms of a tendency of the bonds to be saturated. However, the current microscopic calculations show that the availability of dangling bonds on the topmost silicon atoms is controversial enough
Davydov Splitting in the Absorption Spectra of Molecular Crystals
Molecular Crystals and Liquid Crystals, 1975
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