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E. V. Tkalya

Publications and source records attributed to E. V. Tkalya.

24 records · Page 2Linked to original sources
arXiv2010

Electron Capture $β$-Decay of $^7$Be Encapsulated in C$_{60}$: Origin of Increased Electron Density at the $^7$Be Nucleus

We offer a new theoretical interpretation for the effect of enhanced electron density at $^7$Be nucleus encapsulated in fullerene C$_{60}$. Our {\it{ab initio}} Hartree-Fock calculations show that electron density at the $^7$Be nucleus in $^7$Be@C$_{60}$ increase due to {\it{}attractive} effective potential well generated by the fullerene. The 2$s$ state in the isolated Be atom turns into 3$s$ state in the joint potential. This new state has higher energy, and slightly larger amplitude at the Be nucleus than the previous 2$s$ state. Moreover the 3$s$ wave function has additional {\it{}node} appeared at the distance $r \simeq 5a_B$ from the center. The node imitates repulsion between the Be electron and the fullerene wall, because the electron has zero probability to occupy this region. Such imitation of the repulsion by means of the node in attractive potential has direct physical analogy in the theory of $α$-$α$ and $N$-$N$ nuclear interactions.

nucl-th↗
arXiv2008

Electronic and transport properties of rectangular graphene macromolecules and zigzag carbon nanotubes of finite length

We study one dimensional (1D) carbon ribbons with the armchair edges and the zigzag carbon nanotubes and their counterparts with finite length (0D) in the framework of the Hückel model. We prove that a 1D carbon ribbon is metallic if its width (the number of carbon rings) is equal to $2+3n$. We show that the dispersion law (electron band energy) of a 1D metallic ribbon or a 1D metallic carbon nanotube has a universal {\it sin-}like dependence at the Fermi energy which is independent of its width. We find that in case of metallic graphene ribbons of finite length (rectangular graphene macromolecules) or nanotubes of finite length the discrete energy spectrum in the vicinity of $\varepsilon=0$ (Fermi energy) can be obtained exactly by selecting levels from the same dispersion law. In case of a semiconducting graphene macromolecule or a semiconducting nanotube of finite length the positions of energy levels around the energy gap can be approximated with a good accuracy. The electron spectrum of 0D carbon structures often include additional states at energy $\varepsilon=0$, which are localized on zigzag edges and do not contribute to the volume conductivity.

cond-mat.mes-hall↗
arXiv2007

Theoretical study of molecular electronic excitations and optical transitions of C60

We report results on ab initio calculations of excited states of the fullerene molecule by using configuration interaction (CI) approach with singly excited determinants (SCI). We have used both the experimental geometry and the one optimized by the density functional method and worked with basis sets at the cc-pVTZ and aug-cc-pVTZ level. Contrary to the early SCI semiempirical calculations, we find that two lowest $^1 T_{1u} \leftarrow {}^1 A_g$ electron optical lines are situated at relatively high energies of ~5.8 eV (214 nm) and ~6.3 eV (197 nm). These two lines originate from two $^1 T_{1u} \leftarrow {}^1 A_g$ transitions: from HOMO to (LUMO+1) ($6h_u \to 3t_{1g}$) and from (HOMO--1) to LUMO ($10h_g \to 7t_{1u}$). The lowest molecular excitation, which is the $1 ^3 T_{2g}$ level, is found at ~2.5 eV. Inclusion of doubly excited determinants (SDCI) leads only to minor corrections to this picture. We discuss possible assignment of absorption bands at energies smaller than 5.8 eV (or $λ$ larger than 214 nm).

cond-mat.str-el↗
arXiv2007

Theory of the nuclear excitation by electron transition process near the K-edge

We propose a model for description of the process of Nuclear Excitation by Electron Transition (NEET) near the $K$-shell ionization threshold of an atom. We explain the experimental results for the $^{197}$Au cross section excitation $σ_{N^*}$ obtained by S.Kishimoto et al. Phys. Rev. C {\bf 74}, 031301(R) (2006) using synchrotron radiation near the Au $K$-edge. We predict the behavior of $σ_{N^*}$ as a function of the incident photon energy for nuclei $^{193}$Ir and $^{189}$Os. We reveal that the $^{189}$Os excitation begins when the energy of incident photons is below the $K$-shell ionization threshold in Os.

nucl-th↗
arXiv2005

Manifestation of the cyclo-toroid nuclear moment in anomalous conversion and Lamb shift

We offer the hypothesis that atomic nuclei, nucleons, and atoms possess a new type of electromagnetic moment, that we call a ``cyclo-toroid moment''. In nuclei, this moment arises when the toroid dipole (anapole) moments are arrayed in the form of a ring, or, equivalently, when the magnetic moments of the nucleons are arranged in the form of rings which, in turn, constitute the surface of a torus. We establish theoretically that the cyclo-toroid moment plays a role in the processes of the atomic shell--nucleus interaction. The existence of this moment would explain known anomalies in the internal conversion coefficients for $M1$ transitions in nuclei. We show also that the static cyclo-toroid nuclear moment interacts locally inside the nucleus with the vortex part of the atomic electron currents and this leads to an energy shift in atomic $s_{1/2}$ states. For the hydrogen atom the value of this shift may be comparable in order of magnitude to the present accuracy of measurements of the Lamb shift for the $1s_{1/2}$ level.

nucl-th↗