arXiv subjects

O. I. Obolensky

Publications and source records attributed to O. I. Obolensky.

5 recordsLinked to original sources

arXiv2008

Rigorous treatment of electrostatics for spatially varying dielectrics based on energy minimization

A novel energy minimization formulation of electrostatics that allows computation of the electrostatic energy and forces to any desired accuracy in a system with arbitrary dielectric properties is presented. An integral equation for the scalar charge density is derived from an energy functional of the polarization vector field. This energy functional represents the true energy of the system even in non-equilibrium states. Arbitrary accuracy is achieved by solving the integral equation for the charge density via a series expansion in terms of the equation's kernel, which depends only on the geometry of the dielectrics. The streamlined formalism operates with volume charge distributions only, not resorting to introducing surface charges by hand. Therefore, it can be applied to any spatial variation of the dielectric susceptibility, which is of particular importance in applications to biomolecular systems. The simplicity of application of the formalism to real problems is shown with analytical and numerical examples.

physics.class-ph↗

arXiv2008

Ion-induced electron production in tissue-like media and DNA damage mechanisms

We propose an inclusive approach for calculating characteristics of secondary electrons produced by ions/protons in tissue-like media. This approach is based on an analysis of the projectile's interaction with the medium on the microscopic level. It allows us to obtain the energy spectrum and abundance of secondary electrons as functions of the projectile kinetic energy. The physical information obtained in this analysis is related to biological processes responsible for the irrepearable DNA damage induced by the projectile. In particular, we consider double strand breaks of DNA caused by secondary electrons and free radicals, and local heating in the ion's track. The heating may enhance the biological effectiveness of electron/free radical interactions with the DNA and may even be considered as an independent mechanism of DNA damage. Numerical estimates are performed for the case of carbon-ion beams. The obtained dose-depth curves are compared with results of the MCHIT model based on the GEANT4 toolkit.

physics.bio-ph↗

arXiv2005

T-shaped dimer of coronene

An evidence of importance of the T-shaped configuration of coronene dimer is presented. That is, the dimer's lowest energy configuration is not necessarily a stack, as it might had been expected a priori. This is a surprising result for dimer of such a large polycyclic aromatic hydrocarbon (PAH) as coronene. The energy of the T-shaped configuration at all considered levels of density functional theory (B3LYP,PBE/6-31+G(d),D95,cc-pVDZ,cc-pVTZ) was systematically lower than the energies of three plausible stack configurations. In order to get a better description of the van der Waals interaction,the density functional theory (DFT) results were adjusted by adding a phenomenological Lennard-Jones-type term into the total energy of the system. However, the van der Waals correction is somewhat arbitrary and its magnitude can not be rigorously justified. Depending on the choice of the parameters in the phenomenological term both the T-shaped and the parallel-displaced (PD) stack configurations can be the global energy minimum of the system. A simple model is proposed which is useful for qualitative understanding of possible geometries of the coronene dimer and larger coronene clusters. The model represents coronene dimer as two sets of charged rings interacting via Coulomb and Lennard-Jones potentials. The model provides an intuitively clear explanation why the T-shaped dimers can be of importance even for some of moderately large PAHs such as coronene and, may be, for circumcoronene.

physics.atm-clus↗

arXiv2005

Geometrical and statistical factors in fission of small metal clusters

Fission of metastable charged univalent metal clusters has been studied on example of Na_{10}^{2+} and Na_{18}^{2+} clusters by means of density functional theory methods. Energetics of the process, i.e. dissociation energies and fission barriers, as well as its dynamics, i.e. fission pathways, have been analyzed. The dissociation energies and fission barriers have been calculated for the full range of fission channels for the Na_{10}^{2+} cluster. The impact of cluster structure on the fission process has been elucidated. The calculations show that the geometry of the smaller fragment and geometry of its immediate neighborhood in the larger fragment play a leading role in defining the fission barrier height. The present study demonstrates importance of rearrangement of the cluster structure during fission. It may include forming a neck between the two fragments or fissioning via another isomer state of the parent cluster; examples of such processes are given. For several low-lying isomers of Na_{10}^{2+} cluster the potential barriers for transitions between these isomer states are calculated and compared with the corresponding fission barriers. These data suggest that there is a competition between "direct" fission and fission going via intermediate isomer states of the parent cluster. An impact of the cluster geometry on the change of the system's entropy due to fission is also discussed.

physics.atm-clus↗

arXiv2003

Rearrangement of cluster structure during fission processes

Results of molecular dynamics simulations of fission reactions $Na_{10}^{2+} \to Na_7^+ + Na_3^+$ and $Na_{18}^{2+} \to 2 Na_9^+$ are presented. Dependence of the fission barriers on isomer structure of the parent cluster is analyzed. It is demonstrated that the energy necessary for removing homothetic groups of atoms from the parent cluster is largely independent of the isomer form of the parent cluster. Importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual separation of the daughter fragments begins and/or forming a "neck" between the separating fragments.

physics.atm-clus↗