O. R. Rakhmanova

Computational study of interaction of bromine ions with clusters (O2)6(H2O)50 and (O3)6(H2O)50

Interaction of bromine ions with water clusters that have absorbed the molecules of oxygen and ozone is studied using a molecular-dynamics simulation of flexible molecules. The cases of location of Br− ions on the surface and in the bulk of the cluster are described. Water clusters with ozone molecules remain stable during their interaction with the Br− ions, while oxygen molecules are found to evaporate from the cluster when Br− ions appear in its bulk. In the presence of Br− ions, the infrared spectra of systems with O3 molecules are observed to be intensified. The intensities of the IR spectra with O2 molecules may both increase and decrease depending on the arrangement of the Br− ions. The Raman spectra are sensitive to the appearance of Br− ions only for systems that contain oxygen molecules. As a result of interaction with the Br− ions, the power of IR radiation emitted by the clusters can not only increase, but also decrease.

Molecular-dynamic modeling of the spectral characteristics of the ozone-water cluster system

The absorption of one to six ozone molecules by the (H2O)25 cluster is studied by the method of molecular dynamics under near-atmospheric conditions. The capture of O3 molecules by a water cluster produces a decrease in the integral intensity of IR absorption, reflection, and Raman spectra. IR absorption spectra are highly sensitive to the number of ozone molecules absorbed by a water cluster. The observed photon emission time and the radiation intensity of a dispersed aqueous system with absorbed ozone molecules are appreciably reduced relative to the analogous characteristics of a pure water cluster system.

Numerical simulation of heating an aluminum film on two-layer graphene

The behavior of a monolayer aluminum film on two-layer graphene upon heating from 300 to 3300 K was studied by the molecular dynamics method. A stretched film is nonuniformly contracted with an increase in temperature. Aluminum atoms remain on graphene even at 3300 K. Heating reduces stresses in the film plane. Upon heating to 3000 K, the long-range order in graphene is transformed into the mid-range one. The increase in the intensity of vertical displacements of C atoms in one graphene sheet (caused by an increase in temperature) generally reduces the corresponding intensity in the other sheet, whereas the horizontal components of mobility, with few exceptions, behave similarly. Upon heating, stresses in the upper graphene sheet decrease with different rates for different directions.

The Structure of Water Clusters Interacting with Gaseous Acetylene

The interaction of water clusters with acetylene molecules at T = 230 K was studied by the molecular dynamics method. The structure of clusters was analyzed by constructing Voronoi polyhedra. Water clusters interacting with C2H2 molecules are characterized by a diversity of H-bond orientations, a more uniform distribution of H-bonds over the cluster volume, a larger number of bonds per atom, and smaller bond lengths. The spectrum of bond lengths broadens as the number of acetylene molecules interacting with the water cluster increases. C2H2 molecules have a pressing action on water clusters.

Temperature Changes of the Optical Properties of (SiO 2 ) n , (GaAs) m , and (SiO 2 ) n (GaAs) m Nanoparticles: Computer Experiment

The optical properties of silicon dioxide and gallium arsenide nanoparticles and the four-component particles based on them were calculated by the molecular dynamics method. The complex dielectric permittivity, infrared and Raman spectra, refractive index, and absorption coefficient of these nano particles were determined. The temperature dependences of the infrared and Raman spectra and the number of the optically active electrons in the nanoparticles composed of a semiconductor and/or a dielectric were investigated.

Computer simulation of the structure of water clusters containing absorbed ethane molecules

The structure of water clusters that have absorbed ethane molecules is studied by the molecular dynamics method. Structural analysis is performed by the construction of Voronoi polyheda for oxygen atoms and hybrid polyheda whose centers coincide with the centers of oxygen atoms and the faces are formed according to the positions of hydrogen atoms. The (H2O)20 cluster can retain no more than four ethane molecules remaining at the same time stable. When a water cluster adds more than four ethane molecules, the volumes of Voronoi polyheda acquire values close to the volume per molecule in the bulk liquid water. As the number of ethane molecules in a water cluster increases, the number of hydrogen atoms adjacent to oxygen, as well as the average number of units in cyclic formations composed of hydrogen atoms, also increases. In this case, the number of H-O-H angles formed by the nearest geometric neighbors close to 89° becomes dominant. The coefficient of nonsphericity reflecting the local arrangement of hydrogen atoms around the oxygen atoms decreases as the C2H6 molecules are added to water cluster and approaches to the value of this coefficient for the rhombic dodecahedron in the case of adsorption of six ethane molecules.

Computer simulation of a forced drift of lithium ions through graphene membranes

A drift of Li+ ions upon electric interactions in a planar channel formed by graphene sheets and a cell separated by two graphene membranes with pores of various types has been investigated by the molecular dynamics method. The optimal size of the planar channel gap is determined based on the character of the ion dynamics and the ion effect on the physical properties of the graphene sheets. A set of graphene sheets with divacancies demonstrates the best throughput of lithium ions among six sets of membrane pairs. The ions passing through the membrane are found to affect the kinetic characteristics of the graphene membranes.

Computer-assisted study of characteristics of water clusters in the presence of nitrogen dioxide

The interaction of IR radiation with water clusters that have absorbed NO2 molecules is studied by the molecular dynamics method in terms of the polarizable model. Induced dipole moments of H2O and NO2 molecules diminish during the addition of one to six NO2 molecules to (H2O)50 cluster. The integral intensity of IR absorption by a system consisting of (NO2)i(H2O)50 heteroclusters with 1 ≤ i ≤ 6 decreases, whereas the power of heat emission rises as compared with an (H2O)n system. The decrease in the IR absorption and the increase in the IR emission by water clusters with the capture of NO2 molecules are nonmonotonic. The absorption of NO2 molecules by water clusters causes a noticeable reduction in the intensity of the first peak and the confluence of the fourth and fifth peaks in the Raman spectrum.

IR Absorption and Raman Spectra of Silicon Dioxide Nanoparticles in the Presence of Water: Computer Experiment

Interactions of (SiO2)50 clusters with 10, 20, 30, or 40 water molecules are studied by molecular dynamics method. Flat SiO2 nanoparticle covered with a water layer is formed after the inclusion of water molecules into the cluster. As a rule, the integral intensity of IR and Raman spectra lowers after the absorption of H2O molecules by the cluster. The power of IR radiation emitted by the cluster increases nonmonotonically with the addition of water molecules to the cluster. The absorption of water molecules by the cluster leads to a significant increase in the absorption coefficient and only a slight increase in the refractive index. The number of electrons participating in the interaction with electromagnetic radiation increases with the addition of water molecules to the cluster.

Spectral effects of the clusterization of greenhouse gases : Computer experiment

Autocorrelation functions of the total dipole moment of clusters composed of H2O and N2O molecules are calculated in terms of the molecular dynamics method. The IR absorption and reflection spectra of systems composed of (H2O)i, N2O(H2O)i, and (N2O)2(H2O)i clusters (2 ≤ i ≤ 20) are obtained on the basis of these functions. Frequency-dependent dielectric permittivity of clusters increases after the absorption of N2O molecules. The absorption coefficient of cluster systems with trapped N2O molecules increases at low frequencies and decays at frequencies ω > 500 cm−1. The inclusion of N2O molecules increases also reflection coefficient R and changes the pattern of R(ω) spectra. The absorption of IR radiation increases with the number of H2O molecules in clusters. Dielectric losses also increase with an increase in i number upon the absorption of N2O molecules. The number of electrons interacting with an incident electromagnetic wave increases upon the capture of N2O molecules.