Crystal field and first principle calculation of optical and electronic properties of ZnCr₂O₄ spinel

In the present work we report on combined methods for calculation of optical energy levels scheme and electronic properties of antiferromagnetic spinel ZnCr2O4. The exchange charge model (ECM) was used to calculate the crystal field parameters (CFP) with taking into account the effects of the covalent bond formation between the Cr3+ and O2- ions. The calculated CFP values were used for diagonalization of the Cr3+ Hamiltonian in a complete basis set spanned by all wave functions of the LS terms of 3d3 electron configuration. Ab initio calculations (with the CRYSTAL09 computer program) of the density of states allowed evaluating contribution of each ion into the calculated bands. In addition, the spin-polarized calculations allowed for finding difference between densities of the spin-up and spin-down states of 6-fold coordinated Cr3+ ion. The obtained results are discussed and compared with experimental data.