PhC-2022

I.S. Zamulin, A.A. Gilubnichiy, I.V. Chepkasov, V.S. Baidyshev
Katanov Khakass State University

Abstract: Using modern calculations from first principles, in this work we systematically studied the adsorption of atomic oxygen on the surface of nanoparticles of fcc metals Ag, Cu, Pd consisting of 79 atoms. Two models were considered to describe the reactivity of transition metals based on the d-band center of surface atoms, as well as on the basis of the generalized coordination number. Both methods for predicting the adsorption energy of oxygen atoms at different sites have shown good results, however, the method based on the generalized coordination number is computationally simpler, since this method requires information only about the structure of the particle, while the d-band center model requires electronic structure calculations. The obtained values of the oxygen adsorption energy and d-band center correspond to the known literature data. The most favorable positions for the adsorption of an oxygen atom are on the (100) plane and are hollow consisting of 4 atoms and do not depend on the type of metal under consideration. The highest adsorption energy of the oxygen atom was observed in the case of copper nanoparticles.
Keywords: transition metals, nanoparticles, generalized coordination number, adsorption, electron density functional theory

I.V. Talyzin¹, V.M. Samsonov¹, S.S. Bogdanov¹, N.Yu.. Sdobnyakov¹, R.E. Grigoryev¹, A.V. Pervikov², I.V. Mishakov^3
1 Tver State University
² Institute of Strength Physics and Materials Science of Siberian Branch of Russian Academy of Sciences
³ Federal Research Center Boreskov Institute of Catalysis

Abstract: The paper is devoted to the substantiation and further development of the approach to the analysis of the mesoscopic and integral structure of binary metal nanoparticles from the radial distributions of the local density of the components. As an example, the local density distributions of Ni and Al obtained using the results of molecular dynamics modeling of binary Ni-Al nanoparticles with an initial uniform distribution of components and Ni@Al core-shell icosahedral nanostructures are considered. Both patterns demonstrate the surface segregation of Al atoms during relaxation and subsequent quenching of the initial configurations containing 5000 atoms in 1:1 ratio (nanoparticle radius 3 nm). During cooling, the temperature of the nanoparticles decreased from 1000 K to 0,01 K with a low for atomistic simulation cooling rate. Experimentally binary Ni-Al nanoparticles with a radius of about 100 nm (76Ni:24Al at.%) were synthesized by the wire electric explosion. The experimental intensity distributions obtained from the data of energy-dispersive analysis under the action of an electron beam are presented and analyzed. These distributions correspond to a greater extent to the initial configurations in our molecular dynamics experiments, i.e., they are obviously nonequilibrium. At the same time, it was concluded that the final molecular dynamic configurations are also not entirely equilibrium.
Keywords: core-shell nanostructures, Ni-Al nanoparticles, radial density distributions, embedded atom method, tight binding potential, molecular dynamics, wire electric explosion method, energy- dispersive analysis

A.V. Tvardovskiy
Rector of Tver State Technical University

Abstract: Up to the present time, the construction of a general theory of the equilibrium adsorption is a very urgent task. In the present paper, a general phenomenological approach is developed to describe both adsorption and absorption equilibria. It was shown that under certain assumptions, the resulting equation transforms into the well-known classical Henry, Langmuir, Brunauer-Emmett-Teller equations with constants having a clear physical meaning. Thus, the constant in the Henry equation is determined by the temperature, the specific surface of the adsorbent, the size of the adsorbate molecules, the molar mass of the adsorbate and the isosteric heat of adsorption (the energy of interaction of the adsorbate molecules with the surface of the adsorbent). In the derived Brunauer-Emmett-Teller partial equation, in contrast to the classical version, a clear dependence of the equation constant on the specific physical characteristics of the adsorption system is indicated for the first time. It is determined by the concentration of adsorbate molecules in the liquid phase at the temperature under consideration, the concentration of adsorbate molecules during the formation of a dense monolayer on the surface of the adsorbent, the energy of interaction of adsorbate molecules with the
surface of the adsorbent and the heat of condensation. The presented approach can serve as a basis for modeling a variety of adsorption and absorption phenomena, including adsorption on microporous adsorbents.
Keywords: adsorption, adsorbent, absorption, thermodynamics of phase equilibria, Henry equation, Langmuir equation, Brunauer–Emmett–Teller equation

V.M. Yurov, V.S. Portnov, A.D. Mausymbayeva
Karaganda Technical University

Abstract: The aim of the work is to build a model of the surface layer of objects (crystals) and to elucidate the role of surface energy in physical processes occurring in the nanoscale region. Frame hydrocarbons of the adamantane type, which have a highly symmetrical diamond-like structure, were chosen as objects. On the basis of an empirical model, the thickness of the surface layer and the surface energy of framework hydrocarbons were determined for the first time. In practice, this is very important, since all physical and chemical processes significant in operation occur through the surface layer. For adamantane, the thickness of this layer is 21.6 nm, and for diamond it is 8.2 nm, that is, they represent a nanostructure. Such a difference in the thickness of the surface layer of the two types of structures causes their sharp difference in their properties, in particular, in their surface energy, which determines their mechanical properties. For adamantane, the surface energy is 378.7 mJ/m2, and for diamond it is 9400 mJ/m2. In practice, researchers have found that under shock-wave action, the degree of adamantane→diamond transformation is almost 30%. The work of adhesion for frame hydrocarbons is 400–500 mJ/m2, and internal stresses are 35–45 MPa, which in the surface layer lead to a decrease in adhesive strength and the inverse Hall-Petch effect.
Keywords: surface layer, nanostructure, surface energy, atomic volume, size effect, hydrocarbon, adamantane, diamond, empirical model

E. Andre, A.N. Tsirulev
Tver State University

Abstract: The model of universal quantum computation, which uses quantum circuits consisting of one-qubit and two-qubit logic elements, is implemented in several existing quantum-computing devices. In the last decade, the idea of using multiqubit gates has become very relevant, since this, in the future, will reduce the noise level of quantum circuits. The main resource of quantum computing is the entanglement of individual qubits that form a cluster. Despite the actuality of this issue, so far only a few examples of the simplest logic elements with entanglement are considered in theory for a system of three qubits (Toffoli element and double controlled NOT). This work is devoted to mathematical modeling of the entangled states of quantum systems composed of several qubits. A mathematical method is proposed for the exact or approximate construction of Hamiltonians generating the required unitary transformations. It turns out that the approach based on the representation of Hamiltonians and unitary transformations in the Pauli basis is the most suitable in this context for two reasons: firstly, the Pauli basis forms the Lie algebra of the corresponding unitary group; secondly, there are only real coefficients in the decompositions of Hamiltonians and state density operators in this basis. The method is considered in detail on the example of a three-qubit cluster driven by a ternary Hamiltonian to obtain the Greenberger-Horn-Zeilinger entangled state. For this system, the thermal state is also studied and the corresponding density operator is obtained.
Keywords: quantum gate, quantum entangled state, unitary transformation, decomposition of Hamiltonian, Pauli basis, Greenberger-Horn-Zeilinger state

A.A. Blinova, A.V. Blinov, M.A. Pirogov, K.A. Ogurkov, D.G. Maglakelidze, A.A. Yakovenko
North Caucasus Federal University

Abstract: In this work, a quantum-chemical modeling of the process of interaction of calcium phosphate with amino acids was carried out. Within the framework of the quantum chemical modeling, the total energy of the molecular complex E, the energy difference between the amino acid molecule, and the «calcium phosphate – amino acid» system ∆E, the energy of the highest occupied molecular orbital E_HOMO, the energy of the lowest free molecular orbital E_LUMO, and the chemical rigidity of the system η were calculated. In this work, 8 essential proteinogenic amino acids were considered as stabilizers. As a result of the data analysis, it is found that all the presented interactions are energetically favorable: ∆E > 3370 kcal/mol, and the chemical rigidity of these interactions is in the range from 0,049 to 0,090 eV. Based on the obtained data, the most stable and energetically favorable interaction is the «calcium phosphate – Lys» system (∆E = 3395,848 ± 0,151 kcal/mol, η = 0,085 ± 0,006 eV). To confirm the data obtained, the samples were examined by IR spectroscopy. It has been established that the interaction of the amino acid lysine with the surface of a calcium phosphate particle occurs when oxygen is bound to amino groups in the lysine molecule.
Keywords: quantum chemical modeling, calcium phosphate, valine, leucine, isoleucine, methionine, threonine, lysine, phenylalanine, tryptophan, chemical rigidity, IR spectroscopy method, total energy of the molecular complex

S.A. Vasilyev, V.V. Puitov, I.V. Talyzin, V.M. Samsonov
Tver State University

Abstract: A comparative molecular dynamics simulation of the gas-phase synthesis of Ag nanoparticles is carried out employing two different types of many-particle potentials of the interatomic interaction: a potential corresponding to the embedded atom method and the tight-binding potential. The initial temperature was varied from 1000 to 3000 K, and then it gradually decreased to 77 K, which corresponded to the temperature of liquid nitrogen. The results obtained using alternative force fields are consistent with each other, but, at the same time, they significantly differ both in the dynamics of evolution of the system and in the
obtained final configurations of nanoparticles. Increasing the cutoff radius of the tight binding potential significantly changes the rate of the nanoparticle formation. However, an increase in the cutoff radius when using the embedded atom method does not affect the evolution of the system. The configurations obtained as a result of simulation using the embedded atom method are characterized by a smaller size and a shape close to spherical, while when using the tight binding potential, larger nanocrystals with an elongated shape are formed.
Keywords: silver nanoparticles, gas-phase synthesis, embedded atom method, tight binding potential, molecular dynamics

S.A. Veresov, K.G. Savina, A.D. Veselov, S.V. Serov, A.Yu.. Kolosov, V.S. Myasnichenko, N.Yu.. Sdobnyakov, D.N. Sokolov
Tver State University

Abstract: Various types of configurations of the Au-Cu-Pd-Pt four-component nanosystem, including complex core-shell structures, have been studied. The Monte Carlo method was used as a simulation method, the interatomic interaction was described by the tight-binding potential, i.e. the Gupta potential. According to the results of a series of computer experiments, it was found that four-component nanoparticles of this system do not tend to form a core-shell structure, even though gold atoms have an increased surface segregation. The melting temperatures for the nanosystems under study have been determined. The obtained values are in the range from 1100 K to 1250 K and weakly depend on the composition of nanoparticles (the ratio of the number of atoms). A stoichiometric composition based on these metals was found, for which, during cooling, an FCC crystal structure with inclusions of the HCP phase is formed. However, no distinctive features in the nature of segregation for this stoichiometric composition have been established. All considered stoichiometric compositions in the studied temperature range were stable with respect to decomposition.
Keywords: Monte Carlo method, tight-binding potential, four-component nanoparticles, structure formation, melting temperature, stability

V.S. Myasnichenko, D.N. Sokolov, A.N. Bazulev, N.I. Nepsha, P.M. Ershov, N.Yu.. Sdobnyakov
Tver State University

Abstract: Based on the Metropolis software, a lattice statistical model of the layer-by-layer growth of bimetallic nanoparticles has been implemented. As an example, this paper analyzes two types of lattices: fcc and decahedral. On their basis, the growth of free Au-Ag nanoparticles is modeled in three modes that differ in growth stages: 3, 4, or 7 bimetallic layers are added. The interatomic interaction is set by the tight-binding potential, however, the constructed model does not exclude the possibility of using other modifications of the proven many-particle potentials. The change in the specific potential energy of entire nanoparticles and gold atoms during layer-by-layer growth is analyzed. The dependence of the number of mixed bonds on the layer number is studied for the entire nanoparticle and for the gold subsystem.
Keywords: computer experiment, Monte Carlo method, Metropolis scheme, layer-by-layer growth, bimetallic nanoparticles, mixed bonds

D.A. Ryzhkova, S.L. Gafner, Yu..Ya.. Gafner, A.A. Cherepovskaya
KatanovKhakas State University

Abstract: Silver nanoclusters with diameter of 3,0 to 7,0 nm were studied by the molecular dynamics method using the tight binding potential TB-SMA (second moment approximation of tight-binding potential). A search was made for the stability limits of structural modifications of these nanoclusters for determination of the size limit of the thermally induced structural transition from the initial amorphous morphology to the fcc phase. The new data were compared with the results of previous studies for Ag nanoparticles up to 2,0 nm in size with initial fcc and amorphous structures. It is shown that the studied nanoclusters can be conditionally divided into three categories. The first one (N < 100 atoms) is characterized by partial preservation of the original morphology. For the second one (d < 4,0 nm), there is competition between the icosahedral and decahedral structures. And for the thirds (d > 4,0 nm), the mixed fcc/hcp phase predominates. In this case, the size limit of the transition from the initial amorphous morphology to the structure characteristic for the bulk matter is a diameter of about 7,0 nm.
Keywords: nanoclusters, silver, computer simulation, structure, tight binding, phase transitions, structural stability