arXiv subjects

L. A. Openov

Publications and source records attributed to L. A. Openov.

At least 19 recordsLinked to original sources

arXiv2017

Negative Poisson's Ratio in Phagraphene

We present the results of numerical simulation of elastic properties of phagraphene, a recently predicted but not synthesized yet quasi-two-dimensional allotrope of graphene. We show that the Poisson'ss ratio is positive for the planar configuration of phagraphene and negative for the nonplanar one. Both the Poisson's ratio and the Young's modulus are isotropic for the planar phagraphene and strongly anisotropic for the nonplanar phagraphene.

cond-mat.mes-hall↗

arXiv2016

Thermal Stability of Diamond-Like Carbon Nanothreads

The thermally activated fracture processes in the carbon backbone of diamond-like carbon nanothreads and the hydrogen desorption from them has been studied by the molecular dynamics method. Specifically, the temperature dependence of the characteristic desorption time at T = 1700-2800 K has been determined. The activation energy and frequency factor in the Arrhenius formula for the desorption rate are found. This allows estimating the desorption time at any temperature. The mechanical stiffness of nanothreads is calculated.

cond-mat.mes-hall↗

arXiv2016

Possible nonplanar structure of phagraphene and its thermal stability

It is shown that phagraphene, a recently predicted planar allotrope of graphene with Dirac fermions, is unstable or, at least, almost unstable with respect to transverse atomic displacements. This result is obtained by numerical calculations in the framework of both the tight-binding model and the density functional theory. A nonplanar atomic configuration of phagraphene has a wavy shape and is almost degenerate in energy with the planar configuration. The main types of possible structural defects in phagraphene are determined. The temperature dependence of characteristic times of their formation is found.

cond-mat.mes-hall↗

arXiv2015

Attraction between topological defects in graphene

The interaction of Stone-Wales topological defects in graphene has been studied through computer simulation. This simulation has revealed configurations of two defects with energies below the energy of a monolayer with two spaced defects. This indicates the attraction between defects and the possibility of the formation of their clusters. The attraction is due to the interference between defect-induced wavy distortions of the structure of the monolayer. In this case, the amplitude of transverse displacement of atoms near a pair of defects reaches 2-3 angstroms. Such a strong deformation of graphene by Stone-Wales defects can be one of the reasons for its experimentally observed "crumpled" texture.

cond-mat.mes-hall↗

arXiv2015

Real-time evolution of the buckled Stone-Wales defect in graphene

Dynamics of the buckled Stone-Wales defect in graphene is studied by means of computer simulation. Thermally activated switching between two degenerate sine-wave-like configurations of the defect is traced in real time. Transition trajectory is found to be rather complex and pass through a multitude of near-planar, wave-like, and irregular configurations. Surprisingly, the switching time fluctuates strongly and can be up to an order of magnitude longer or shorter than the value given by the Arrhenius formula. This is due to a peculiar shape of the potential relief in the neighborhood of sine-wave-like configurations and, as a result, the occurrence of two radically different characteristic times.

cond-mat.mes-hall↗

arXiv2014

On the Vineyard Formula for the Pre-Exponential Factor in the Arrhenius Law

By the example of several typical thermally activated processes in atomic clusters, organic molecules, and nanostructures, it is shown that calculations of the corresponding pre-exponential factors in the Arrhenius law according to the Vineyard formula are in good agreement with the molecular dynamics simulation data for temperature dependences of characteristic times of these processes. This "static" approach (together with the determination of the activation energy through the examination of the potential energy hypersurface) provides information on kinetic characteristics of the system without resorting to numerical simulation of the time evolution, which requires large computer resources.

cond-mat.mes-hall↗

arXiv2011

Thermal Stability of C4+4nH8 Polycubanes

The temperature dependences of the lifetimes of polycubanes C4+4nH8 with n = 2 - 5 up to their decomposition have been directly calculated using the molecular dynamics method. It has been shown that the activation energy of decomposition of these metastable clusters, in which the C-C bonds form an angle of 90^0 that is not characteristic of carbon systems, rapidly decreases with an increase in n due to the lowering of the energy barrier that prevents the decomposition of the clusters. This has cast some doubt on the recently made suggestion that there exist nanotubes (n >> 1) with a square cross section. Nonetheless, the stability of bicubane (n = 2) and tricubane (n = 3) has proved to be sufficient for their existence at the liquid-nitrogen temperature.

cond-mat.other↗

arXiv2011

On the Thermal Stability of Graphone

Molecular dynamics simulation is used to study thermally activated migration of hydrogen atoms in graphone, a magnetic semiconductor formed of a graphene monolayer with one side covered with hydrogen so that hydrogen atoms are adsorbed on each other carbon atom only. The temperature dependence of the characteristic time of disordering of graphone via hopping of hydrogen atoms to neighboring carbon atoms is established directly. The activation energy of this process is found to be Ea=(0.05+-0.01) eV. The small value of Ea points to extremely low thermal stability of graphone, this being a serious handicap for practical use of the material in nanoelectronics.

cond-mat.mes-hall↗

arXiv2010

Thermal Desorption of Hydrogen From Graphene

The process of hydrogen desorption from graphane (graphene sheet saturated by hydrogen adsorbed from both sides) has been studied using the method of molecular dynamics. The temperature dependences of the time of desorption onset for various hydrogen coverages on graphene are calculated and the corresponding activation energies in the Arrhenius equation are determined. It is established that graphane exhibits a rather high thermal stability that makes possible its usein two-dimensional electronics even at room temperature. For the same reason, graphane can hardly be considered as a promising hydrogen storage material for fuel cells.

cond-mat.mes-hall↗

arXiv2010

On the Temperature Dependence of the Lifetime of Thermally Isolated Metastable Clusters

The temperature dependence of the lifetime of the thermally isolated metastable N8 cubane up to its decay into N2 molecules has been calculated by the molecular dynamics method. It has been demonstrated that this dependence significantly deviates from the Arrhenius law. The applicability of the finite heat bath theory to the description of thermally isolated atomic clusters has been proved using statistical analysis of the results obtained.

cond-mat.mes-hall↗

arXiv2009

Spontaneous Regeneration of an Atomically Sharp Graphene/Graphane Interface under Thermal Disordering

The smearing of the graphene/graphane interface due to the thermally activated migration of hydrogen atoms is studied by the molecular dynamics method. Contrary to expectations, it is found that the fast spontaneous regeneration of this interface occurs even at a sufficiently high temperature T about 1500 K. As a result, the average width of the disordered region does not exceed the length of a C-C bond, i.e., the interface remains almost atomically sharp. The cause of this effect appears to be the specific shape of the potential relief of the system, namely, the significant difference between the heights of the energy barriers for the direct and inverse migrations of hydrogen atoms. A simple model that makes it possible to obtain the temperature dependence of the equilibrium distribution function of typical atomic configurations, to estimate the typical time of establishing the equilibrium state, and thereby to quantitatively describe the results of the computer experiment is presented.

cond-mat.mes-hall↗

arXiv2009

Nonorthogonal tight-binding model for hydrocarbons

Parameters of the nonorthogonal tight-binding model for hydrocarbons are derived based on a criterion of the best agreement between the calculated and experimental values of bond lengths and binding energies for different molecules CnHm. The results obtained can be used, e. g., to study the kinetics of hydrogen absorption by carbon nanostructures, to simulate the dynamics of hydrocarbon clusters like cubane C8H8, etc.

cond-mat.other↗

arXiv2009

Thermal stability of cubane C8H8

The reasons for the anomalously high thermal stability of cubane C8H8 and the mechanisms of its decomposition are studied by numerically simulating the dynamics of this metastable cluster at T = 1050 - 2000 K using a tight-binding potential. The decomposition activation energy is found from the temperature dependence of the cubane lifetime obtained from the numerical experiment; this energy is fairly high, Ea = 1.8 - 2.0 eV. The decomposition products are, as a rule, either C6H6 and C2H2 molecules or the isomer C8H8 with a lower energy.

cond-mat.mes-hall↗

arXiv2008

Laser-induced operations with charge qubits in a double-well nanostructure

We present the results of theoretical studies on operations with charge qubits in the system composed of two tunnel-coupled semiconductor quantum dots whose two lowest states (localized in different dots) define the logical qubit states while two excited states (delocalized between the dots) serve for the electron transfer from one dot to another under the influence of the laser pulse. It is shown that in the case of small energy separation between the excited levels, the optimal (from the viewpoint of minimal single-qubit operation time and maximum operation fidelity) strategy is to tune the laser frequency between the excited levels. The pulse parameters for implementation of the quantum NOT operation are determined. Analytical results obtained in the rotating-wave approximation are confirmed by rigorous numerical calculations.

cond-mat.mtrl-sci↗

arXiv2008

Structure and Stability of Two-Dimensional Complexes of C_20 Fullerenes

Two-dimensional complexes of C_20 fullerenes connected to each other by covalent bonds have been studied. Several isomers with different types of intercluster bonds have been revealed. The lifetimes of the (C_20)_MxM systems with M = 2 and 3 have been directly calculated at T = 1800 - 3300 K making use of molecular dynamics. It has been shown that these complexes lose their periodic cluster structure due to either coalescence of two fullerenes C_20 or decay of C_20 fullerenes. The activation energies of these processes exceed 2 eV.

cond-mat.other↗

arXiv2008

Violation of the Equipartition Theorem for Thermally Insulated Clusters of Atoms with Different Masses

An expression is derived for calculating microcanonical-ensemble averages of the kinetic energies of atoms of different types in clusters isolated from the environment. This expression is a natural generalization of the solution to the problem of hard spheres with different masses to a system with a many-particle interatomic interaction potential. The dynamics of a C8H8 cubane is simulated numerically. The data on the numerical simulation confirm the validity of the results obtained.

cond-mat.mes-hall↗

arXiv2008

Phonon-induced decoherence of the two-level quantum subsystem due to relaxation and dephasing processes

Phonon-related decoherence effects in a quantum double-well two-level subsystem coupled to a solid are studied theoretically by the example of deformation phonons. Expressions for the reduced density matrix at T=0 are derived beyond the Markovian approximation by means of explicit solution of the non-stationary Schrodinger equation for the interacting electron-phonon system at the initial stage of its evolution. It is shown that as long as the difference between the energies of the electron in the left and the right well greatly exceeds the energy of the electron tunneling between the minima of the double-well potential, decoherence is primarily due to dephasing processes. This case corresponds to a strongly asymmetric potential and spatially separated eigenfunctions localized in the vicinity of one or another potential minimum. In the opposite case of the symmetric potential, the decoherence stems from the relaxation processes, which may be either "resonant" (at relatively long times) or "nonresonant" (at short times), giving rise to qualitatively different temporal evolution of the electron state. The results obtained are discussed in the context of quantum information processing based on the quantum bits encoded in electron charge degrees of freedom.

cond-mat.other↗

arXiv2007

Stability of C20 fullerene chains

The stability of (C20)N chains with N = 3 - 7 is analyzed by numerical simulation using a tight-binding potential and molecular dynamics. Various channels of losing the cluster-chain structure of the (C20)N complexes are observed, including the decay of C20 clusters, their coalescence, and the separation of one C20 fullerene from the chain.

cond-mat.mes-hall↗