Ab initio modeling of Raman and infrared spectra of calcite

Calcite is the most thermodynamically stable polymorphic phase of the CaCO3 crystal. It is widely used in modern optical instruments operating in the infrared and visible wavelengths of electromagnetic radiation. In particular, due to its anisotropic properties, calcite is used in polarization optics devices. Ab initio quantum mechanical modeling of the Raman and infrared spectra of calcite makes it possible to better understand the structure and nature of the chemical bonds of the compound, and find the optimal conditions for the effective use of unique properties of calcite in photonics tools. The calculations are performed within the framework of the density functional theory in the CRYSTAL program, using the “hybrid” B3LYP functional and the all-electronic bases of the STO-6G, PO-TZVP and BSD atomic orbitals of the Gaussian type. The obtained results for the elastic constants, Raman and infrared spectra of calcite agree satisfactorily with the available experimental data for the basic sets of POB-TZVP and BSD.The work was partially funded by the Ministry of Education and Science of Russia under Competitiveness Enhancement Program of Samara University for 2013-2020, project 3.5093.2017/8.9

On charmonia and charmed mesons photoproduction at high energy

We compare the predictions of the collinear parton model and the k_T-factorization approach in J\Psi and D^\star meson photoproduction at HERA energies. It is shown that obtained in the both approaches D^\star meson spectra over p_T and \eta as well as J\Psi meson p_T- and z-spectra are very different. The predictions obtained in the k_T-factorization approach are agree with the experimental data well. We also predict the nontrivial p_T-dependence of the the spin parameter $\alpha(p_T) in the J\Psi photoproduction.Comment: Talk was presented at International Seminar "Heavy quark - 2002", JINR, Dubna, Russia, May-June, 2002. In version 2 we have corrected numerical results for the D^star meson spectr

From zeolite nets to sp3carbon allotropes: a topology-based multiscale theoretical study

We present a comprehensive computational study of sp3-carbon allotropes based on the topologies proposed for zeolites. From E600000 zeolite nets we identified six new allotropes, lying by at most 0.12 eV per atom above diamond. The analysis of cages in the allotropes has revealed close structural relations to diamond and lonsdaleite phases. Besides the energetic and mechanical stability of new allotropes, three of them show band gaps by ca. 1 eV larger than that of diamond, and therefore represent an interesting technological target as hard and transparent materials. A structural relation of new allotropes to continuous random networks is pointed out and possible engineering from diamond thin films and graphene is suggested

Photoproduction of J/psi mesons at high energies in parton model and k_t-faktorization approach

We consider J/psi meson photoproduction on protons at high energies at the leading order in alpha_s using conventional parton model and k_t-factorization approach of QCD. It is shown that in the both cases the colour singlet mechanism gives correct description for experimental data from HERA for the total cross section and for the J/psi meson z-spectrum at realistic values of a c-quark mass and meson wave function at the origin Psi (0). At the same time our predictions for p_t-spectrum of J/psi meson and for p_t dependence of the spin parameter alpha obtained in k_t-factorization approach are very different from the results obtained in conventional parton model. Such a way the experimental study of a polarized J/psi meson production at the large p_t should be a direct test of BFKL gluons.Comment: LaTeX2e, 11 pages plus 8 fig. using epsfig.st

Heavy Quark Fragmentation into Baryons in a Quark-Diquark Model

In the framework of the nonrelativistic QCD and a quark-diquark model of baryons we have obtained the fragmentation functions for heavy quark to split into spin-1/2 and spin-3/2 double heavy baryons. It was predicted the production rates as well as the shape of the energy spectra for the $cc-$ and $bc-$baryons in the region of $Z^o$ peak at LEP collider.Comment: LaTeX, 9 pages, 2 figure

Direct J/psi and psi' hadroproduction via fragmentation in the collinear parton model and k_T-factorization approach

The p_T-spectra for direct J/psi and psi' in hadroproduction at Tevatron energy have been calculated based on NRQCD formalism and fragmentation approximation in the collinear parton model and k_T-factorization approach. We have described the CDF data and obtained a good agreement between the predictions obtained in the parton model and k_T-factorization approach. We performed the calculations using the relevant leading order in alpha_s hard amplitudes and the equal values of the color-octet long-distance matrix elements for the both models.Comment: 10 pages, Latex, 4 eps figures, epsfig.sty, graphics.st

Simulation of crack growth under mixed-mode loading by molecular dynamics method

Atomistic simulations of the central crack growth process in a plane medium using Large-scale Molecular Massively Parallel Simulator (LAMMPS), a classical molecular dynamics code, are performed. The inter-atomic potential used in this investigation is Embedded Atom Method (EAM) potential. The specimens with initial central crack were subjected to Mixed-Mode loadings. The simulation cell contains 400000 atoms. The crack propagation direction angles under different values of the mixity parameter in a wide range of values from pure tensile loading to pure shear loading in a wide diapason of temperatures (from 0.1 К to 800 К) are obtained and analyzed. It is shown that the crack propagation direction angles obtained by molecular dynamics method coincide with the crack propagation direction angles given by the multi-parameter fracture criteria based on the strain energy density and the multi-parameter description of the crack-tip fields.Financial support from the Russian Foundation of Basic Research (project No. 16-08-00571) is gratefully acknowledged

Production of B(c) mesons via fragmentation in the kT-factorization approach

In the framework of the kT-factorization approach we have calculated in the fragmentation model the pT-spectra of B(c) mesons at the energies of the Tevatron and the LHC Colliders and at the large pT domain. We compare the obtained results with the existing experimental data and with the predictions obtained in the collinear parton model.Comment: 10 pages, 2 figure

Hybrid topology-based computational approach for crystal structure prediction

We propose a theoretical approach for the computational design of new crystal structures. Our approach is based on the analysis of the database(s) which contain(s) hypothetical nets and subsequent multi-scale computations at different levels of theory (from classical potentials to ab initio methods). To work with large databases, containing ~10^6 nets and to find physically adequate crystal structures, we use a set of computer programs: GavrogSystre and ToposPro to manipulate with network topologies and their geometrical relaxation, GULP and DFTB+ for preliminary structure relaxation, VASP and CRYSTAL for accurate ab initio calculations of the main physical properties. Additionally, we apply the CP2K code to check the dynamical stability of the structures at ambient conditions by performing molecular dynamics simulations. We demonstrate the advantages of the proposed approach when using it to predict a few previously unknown sp3 carbon allotropes. For our simulations we use state-of-art parallel computing facilities at the supercomputer of Samara Center for Theoretical Material Science and Supercomputer Center of Samara State Aerospace University