First-principles studies of electronic, optical, and vibrational properties of LaVO₄ polymorph

First-principles calculations of electronic, optical, and vibrational properties of LaVO₄ polymorph were performed with the density functional theory plane-wave pseudopotential method. The results of the electronic structure reveal that the different coordinated structure for monoclinic LaVO₄ leads to an indirect band gap, while tetragonal LaVO₄ has a direct band gap. Besides, the analysis of the electronic structure shows ionic nature in La–O bonds and covalent nature in V–O bonds. From further study in chemical bonding behavior, we find that the V–O covalent bonds have four types: σ bonding, π bonding, π^* antibonding, and σ^* antibonding states. Various optical properties, including the dielectric function, reflectivity, absorption coefficient, refractive index, and the energy-loss spectrum as functions of the photon energy were calculated. Our calculations indicate that monoclinic LaVO₄ has excellent dielectric properties along [0 0 1] direction. In the optical-frequency (ω→∞) contributed from electrons the optical properties of tetragonal LaVO₄ show the isotropy, while the diagonal components of static dielectric tensors ε(0) of tetragonal LaVO₄ have the ε^xx=ε^yy≠ε^zz relation by adding the lattice vibration contribution (ω→0) to the electronic dielectric tensor. The vibrational spectra of LaVO₄ polymorph have also been calculate- - d from first principles by the linear response method. The calculated frequencies are in good agreement with the experimental data available for these crystals obtained by the methods of infrared and Raman spectroscopies. The vibrational spectra of monoclinic and tetragonal LaVO₄ crystal exhibit three groups of frequencies: the low-frequency (<240 cm^-1), middle-frequency (270–450 cm^-1), and high-frequency region (850–970 cm^-1), according to the vibration dominated by translation of La atoms, the bending vibration of O–V–O bonds, and stretching vibration of O–V–O bonds, respectively. Our studies report on microstructure of LaVO₄ polymorph, and provide useful information for the potential application of this material.