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

Abstract

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 εxx=εyy≠εzz relation by adding the lattice vibration contribution (ω→0) to the electronic dielectric tensor. The vibrational spectra of LaVO4 polymorph have also been calculated 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.