Персона: Николаев, Александр Васильевич
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Институт лазерных и плазменных технологий
Стратегическая цель Института ЛаПлаз – стать ведущей научной школой и ядром развития инноваций по лазерным, плазменным, радиационным и ускорительным технологиям, с уникальными образовательными программами, востребованными на российском и мировом рынке образовательных услуг.
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Александр Васильевич
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- ПубликацияТолько метаданныеCharge Properties of Thorium Implanted in Silicon Oxide(2020) Kurelchuk, U. N.; Borisyuk, P. B.; Nikolaev, A. V.; Tkalya, E. V.; Курельчук, Ульяна Николаевна; Борисюк, Петр Викторович; Николаев, Александр Васильевич; Ткаля, Евгений Викторович© 2020, Pleiades Publishing, Ltd.Abstract: A study of thorium atoms implanted in silicon oxide was carried out within the density functional theory method. The charge properties of Th in the ThO2:nSiO2 and Th:nSiO2 compounds, where Th acts as an interstitial and substitutional impurity in cristobalite, have been studied. Geometric optimization of structures is carried out with allowance for electron-electron interactions, self-consistent distribution of electron density is investigated, and Bader effective charges are estimated.
- ПубликацияОткрытый доступСпектроскопическое исследование кристаллических пленок неона, выращенных на золотой подложке(2023) Курельчук, У. Н.; Борисюк, П. В.; Чубунова, Е. В.; Домашенко, М. С.; Каражанов, С. Ж.; Колачевский, Н. Н.; Лебединский, Ю. Ю.; Мызин, Д. А.; Николаев, А. В.; Ткаля, Е. В.; Ткаля, Евгений Викторович; Мызин, Дмитрий Анатольевич; Чубунова, Елена Витальевна; Борисюк, Петр Викторович; Лебединский, Юрий Юрьевич; Николаев, Александр Васильевич; Курельчук, Ульяна НиколаевнаПленка кристаллического неона была конденсирована на подложке из золота и измерен спектр характеристических потерь энергии обратно рассеянных электронов (СХПЭ) при температуре 5К. Также были теоретически исследовано конденсированное ГЦК-состояние неона методами теории функционала плотности и многочастичной теории возмущений, приближения случайных фаз и уравнения Бете−Салпетера. Теоретический спектр СХПЭ был рассчитан как в приближении независимых электронов, так и с учетом многочастичных эффектов – экранирования локального поля, появления электронно-дырочных пар и связанных состояний (экситонов). Получена ширина запрещенной зоны – 21.5 эВ. Показано, что в СХПЭ неона пики потерь энергии от 17.8 до 21.5 эВ являются чисто экситонными. Кристаллическая пленка неона, являясь широкозонным диэлектриком, рассматривается как перспективный материал для имплантации Th и изучения уникального ядерного перехода в 229Th с энергией 8.2 эВ.
- ПубликацияТолько метаданныеSpectroscopic Studies of Crystalline Neon Film Grown on a Gold Surface(2022) Kurelchuk, U. N.; Borisyuk, P. V.; Chubunova, E. V.; Domashenko, M. S.; Kolachevsky, N. N.; Lebedinskii, Yu. Yu.; Myzin, D. A.; Nikolaev, A. V.; Tkalya, E. V.; Курельчук, Ульяна Николаевна; Борисюк, Петр Викторович; Чубунова, Елена Витальевна; Лебединский, Юрий Юрьевич; Мызин, Дмитрий Анатольевич; Николаев, Александр Васильевич; Ткаля, Евгений Викторович
- ПубликацияОткрытый доступEstimation of the charge state of Th implanted in SiO2in the different atomic environment(2020) Kurelchuk, U. N.; Borisyuk, P. V.; Nikolaev, A. V.; Tkalya, E. V.; Курельчук, Ульяна Николаевна; Борисюк, Петр Викторович; Николаев, Александр Васильевич; Ткаля, Евгений Викторович© Published under licence by IOP Publishing Ltd.In this work the investigation of the charge states of thorium implanted in SiO2 is in different atomic environments and at different concentrations is presented.. Th was considered as interstitial and substitutional impurity in model cells of 6, 48 and 96 atoms. The estimations of the Bader effective charges of Th was derived from the electronic charge density n(r) calculated in DFT full relativistic PAW pseudopotential approximation. The change in the electron density of thorium due to the environment in the cells was estimated in comparison with the free atomic state.
- ПубликацияТолько метаданныеMultiple locations of boron atoms in the exohedral and endohedral C60 fullerene(2022) Bodrenko, I. V.; Bibikov, A. V.; Nikolaev, A. V.; Borisyuk, P. V.; Tkalya, E. V.; Николаев, Александр Васильевич; Борисюк, Петр Викторович; Ткаля, Евгений Викторович© 2022 American Physical Society. We study theoretically the bound states of one and two boron atoms in the exohedral and endohedral C60 fullerene. The optimal position of one boron atom is found above the midpoint of the C60 double bond in the exohedral complex, and at the center of C60 or below a carbon atom in the endohedral complex. However, the optimal position of a boron atom is often altered when the second boron atom is added to the molecular complex. For two boron atoms outside the cage the optimal arrangement is realized when the B2 molecule is attached by one boron atom to a double bond midpoint of C60 or when two boron atoms are above two double bond midpoints on opposite sides of C60. Two endohedral boron atoms can lie on the line joining either two opposite double bond midpoints or two centers of opposite pentagons. The latter case corresponds to the optimal geometry of the B2@C60 complex provided that two boron atoms are close enough to form the B2 molecule. In case one boron atom is inside while the other is outside the cage, the optimal locations of atoms are above and below two neighboring carbon atoms belonging to the same hexagon of C60. Remarkably, all these optimal arrangements have different spin states: in the exohedral complex B2C60S=1, in the endohedral B2@C60S=2 (as in the isolated B2 molecule), whereas for one boron atom inside and the other outside the cage S=0. The effective (Bader) charge of boron in these configurations varies appreciably-from 0.06e at the center of C60 to 2e in the B2C58 molecule with two boron atoms substituting for two carbon atoms in C60. We also discuss various conformations in the exohedral and endohedral molecular complexes.
- ПубликацияТолько метаданныеAb initio based description of the unusual increase of the electric field gradient with temperature at Ti sites in rutile TiO2(2020) Chtchelkatchev, N. M.; Salamatin, D. A.; Tsvyashchenko, A. V.; Nikolaev, A. V.; Bibikov, A. V.; Николаев, Александр Васильевич© 2020 American Physical Society.Combining a precise ab initio electron band structure calculation of the TiO2 rutile structure with the temperature evolution of the Ti mean-square displacements, we reproduce a puzzling temperature increase of the electric field gradient at Ti sites in TiO2, observed experimentally. Our method employs a procedure of averaging two quadrupole electron density components (L=2) inside a sphere vibrating with the Ti nucleus at its center, where the key factor introducing the temperature dependence is the square root of the Debye-Waller factor. Although the Debye-Waller factor always reduces the corresponding Fourier component, in TiO2 due to the interplay between terms of opposite signs, it results in a net increase of the whole sum with temperature, leading to the growth of the electric field gradient. Quantitatively, we find that the increase of electric field gradient is only half of the experimental value, which we ascribe to anharmonic effects or a strong oxygen position influence. In addition, our method reproduces the unusual temperature dependence of the asymmetry parameter η, which first decreases with temperature, goes to zero, and then increases.
- ПубликацияТолько метаданныеNeutral and charged thorium impurity in solid argon(2021) Nikolaev, A. V.; Tkalya, E. V.; Николаев, Александр Васильевич; Ткаля, Евгений Викторович©2021 American Physical SocietyWe study the neutral and positively charged thorium impurity (, 1, 2, 3, 4) in solid argon by exploring the nature of chemical bonding in the ThAr diatomic molecule and in clusters at the Hartree-Fock level with the second-order perturbation (MP2) correction accounting for the van der Waals forces. The chemical bonding is formed from the valence states of thorium and polarized states of argon in the clusters with (, 1, 2, 3) and solely from polarized states in the clusters with . In all cases with two or more valence electrons of Th, the ground state, influenced by the first Hund rule for the thorium impurity, is the high spin state. Allowing for the cubic to orthorhombic () symmetry lowering in , we find that the averaged Th-Ar bond length decreases whereas the binding energy increases with , accounted for by the weakening of the Th-Ar repulsion and the strengthening of polarization. For , two conformations (cubic and orthorhombic) are found. We conclude that with the Th-Ar bond lengths lying very close to the Ar-Ar bond lengths in a fcc lattice, the solid argon is a material that is well suited for the accommodation of thorium impurities.
- ПубликацияТолько метаданныеChemical bonding between thorium and novel BN nanomaterials(2022) Kurelchuk, U. N.; Nikolaev, A. V.; Borisyuk, P. V.; Tkalya, E. V.; Курельчук, Ульяна Николаевна; Николаев, Александр Васильевич; Борисюк, Петр Викторович
- ПубликацияТолько метаданныеTowards an ab initio theory for the temperature dependence of electric field gradients in solids: Application to hexagonal lattices of Zn and Cd(2020) Nikolaev, A. V.; Chtchelkatchev, N. M.; Salamatin, D. A.; Tsvyashchenko, A. V.; Николаев, Александр ВасильевичBased on ab initio band-structure calculations we formulate a general theoretical method for description of the temperature dependence of an electric-field gradient in solids. The method employs a procedure of averaging multipole electron-density component (l not equal 0) inside a sphere vibrating with the nucleus at its center. As a result of averaging, each Fourier component (K not equal 0) on the sphere is effectively reduced by the square root of the Debye-Waller factor [exp(-W)]. The electric-field gradient related to a sum of K components most frequently decreases with temperature (T), but under certain conditions because of the interplay between terms of opposite signs, it can also increase with T. The method is applied to calculations of the temperature evolution of the electric-field gradients of pristine zinc and cadmium crystallized in the hexagonal lattice. For calculations within our model, of crucial importance is the temperature dependence of mean-square displacements which can be taken from experiment or obtained from the phonon modes in the harmonic approximation. For the case of Zn, we have used data obtained from single-crystal x-ray diffraction. In addition, for Zn and Cd, we have calculated mean-square displacements with the density-functional perturbation treatment of the QUANTUM ESPRESSO package. With the experimental data for displacements in Zn, our calculations reproduce the temperature dependence of the electric-field gradient very accurately. Within the harmonic approximation of the QUANTUM ESPRESSO package, the decrease in electric-field gradients in Zn and Cd with temperature is overestimated. Our calculations indicate that the anharmonic effects are of considerable importance in the temperature dependence of electric-field gradients.
- ПубликацияОткрытый доступChemical bonding between thorium atoms and a carbon hexagon in carbon nanomaterials(2020) Bibikov, A. V.; Nikolaev, A. V.; Tkalya, E. V.; Николаев, Александр Васильевич; Ткаля, Евгений ВикторовичWe explore the unusual nature of chemical bonding of thorium atoms with a ring of six carbon atoms (hexagon) in novel carbon materials. Our ab initio calculations of Th-based metallofullerenes (Th@C60 and Th@C20) and Th bound to benzene or coronene at the Hartree-Fock level with the second order perturbation (MP2) correction accounting for the van der Waals interactions demonstrate that the optimal position of the thorium atom is where it faces the center of a hexagon and is located at a distance of 2.01-2.07 Å from the center. For Th encapsulated in C60 it is found at 2.01 Å, whereas the other local energy minima are shifted to larger energies (0.22 eV and higher). Inside C60 the highest local minimum at 1.17 eV is observed when Th faces the center of the five member carbon ring (pentagon). Based on our calculations for Th with benzene and coronene where the global minimum for Th corresponds to its position at 2.05 Å (benzene) or 2.02 Å (coronene) from the hexagon center, we conclude that a well pronounced minimum is likely to be present in graphene and in a single wall carbon nanotube. The ground state of Th is singlet, and other high spin states (triplet and quintet) lie higher in energy (>1.62 eV). We discuss a potential use of carbon nanomaterials with the 229Th isotope having its nuclear transition in the optical range, for metrological purposes.