First principles and crystal field calculations of the spectral, structural and electric properties of (Na, Li)VSi_2O6clinopyroxenes crystals

In the present paper we report on the results of theoretical modeling of the structural, spectral and electronic properties of (Na, Li)VSi_2O6clinopyroxenes crystals. At first, the semi-empirical model of crystal field theory, namely, the exchange charge model was employed for modeling the crystal field parameters (CFP), taking into account the effects of the covalent bond formation between the V³⁺and O^2-ions. The calculated CFP values were used for diagonalization of the crystal field Hamiltonian matrix in a complete basis set spanned by all 25 wave functions of the LS terms of the 3d²electron configuration. The second approach, the ab initio density functional theory (DFT)-based calculations, was employed for the structural optimization, analysis of the band structure, density of the states and the pressure effects of the considered compounds. All obtained results are discussed and compared with available experimental data.