Electronic structure and optical properties of β-RbSm(MoO4)2 from spin polarization calculations: DFT+U

We explored the influence of the inclusion of spin polarization on the energy band gap of β-RbSm(MoO4)2. Calculations explored that the appearance of Sm-4f states at the conduction band minimum (CBM) of the spin-up case causes a significant influence on ground state properties of β-RbSm(MoO4)2. The total and partial densities of states confirm the existence of Sm-4f states in the CBM of the spin-up case. The partial densities of states exhibit a strong hybridization between some states which may lead to the formation of covalent bonds. The valence band maximum (VBM) and the CBM are located at the center of first Brillouin zone (Γ), resulting in a direct band gap for both of majority spin (↑) and minority spin (↓). The values of the band gap are 3.01 eV (↑) and 3.78 eV (↓). The all-electron full potential linear augmented plane wave (FPLAPW+lo) method within the generalized gradient approximation plus the Hubbard Hamiltonian (GGA+U) were used. We have applied U on 4f orbital of Sm atoms and 4d orbital of Mo atoms. We have taken a careful look at the electronic charge density distribution to visualize the charge transfer and the chemical bonding characters. The calculated bond lengths show very good agreements with the measured ones. The optical properties were calculated to seek a deep insight into the electronic structure. It has been found that below λ = 450 nm β-RbSm(MoO4)2 exhibits a positive uniaxial anisotropy, while at λ = 450 nm and above, the crystal exhibits a negative uniaxial anisotropy.