Maxim A. Visotin

The electronic structure and spin states of 2D graphene/VX2 (X = S, Se) heterostructures

The structural, magnetic and electronic properties of 2D VX2 (X = S, Se) monolayers and graphene/VX2 heterostructures were studied using a DFT+U approach. It was found that the stability of the 1T phases of VX2 monolayers is linked to strong electron correlation effects. The study of vertical junctions comprising of graphene and VX2 monolayers demonstrated that interlayer interactions lead to the formation of strong spin polarization of both graphene and VX2 fragments while preserving the linear dispersion of graphene-originated bands. It was found that the insertion of Mo atoms between the layers leads to n-doping of graphene with a selective transformation of graphene bands keeping the spin-down Dirac cone intact.

Theoretical Study of the Lithium Diffusion in the Crystalline and Amorphous Silicon as well as on its Surface

Using the PAW DFT-GGA method and numerical solving of master equation the diffusion rates of lithium atoms inside both crystal and amorphous silicon of LixSi (x= 0..0.5) composition have been calculated for different temperatures. It is shown the diffusion rate for amorphous silicon is ~10 times greater than that for the crystal silicon. For both structures the rate is increased by 1.5-2 orders of magnitude while the lithium concentration is increased up to 0.5 value. This should result in that the LixSi/Si interface will be sharp. This fact has been further confirmed using molecular dynamic calculations based on Angular Dependent Potential (ADP) model. Also binding energies of Li atoms lying on different sites of Si (001) surface as well as the potential barriers for the atom jumps both along the surface and in the subsurface layers have been calculated. The data show the Li atoms move along the surface very easily but their jumps into subsurface layers are very difficult due to the high potential barrier values.

Quantum-chemical Research of Endohedral Yttrium Metallofullerenes

Endohedral fullerenes are an interesting class of fullerenes because electron transfer from encaged metal atom to carbon cage has been known to occur and this oftentimes alters the electronic and magnetic properties of the fullerenes [1]. Particularly, endohedral yttrium-fullerenes have been obtained by several research groups [2, 3]. In 1995, Takata and co-workers performed synchrotron X-ray studies on a powder of Y@C82 to confirm the endohedral nature of EMFs for the first time [3]. However, it is still not clear whether the sample contained a pure Y@C82 isomer or if it was a mixture of two or more regioisomers. Nowadays, the structures of new EMFs can be routinely predicted from the first principles (knowing only a formula of the molecule) with the high reliability rivaling that of singlecrystal X-ray diffraction studies [4]. Potential applications of endodedral fullerenes were also predicted on the basis of their peculiar electronic, physical and chemical properties, including superconductors [5], metallofullerene lasers [5] ferroelectric materials [6, 7], nanomemory devices [5] quantum computers, etc. [8].