Dependence of structural, electrical, electronic and optical properties of lithium niobate on the types of pseudopotentials and exchange–correlation functionals: A DFT investigation

Abstract

Within the framework of density functional theory, we used different types of exchange–correlation functionals with the three existing types of pseudopotentials to study the structural, electrical, electronic and optical properties of lithium niobate in its ferroelectric phase. Among the types of exchange–correlation functionals implemented in Quantum Espresso, we considered twenty-eight types in the present study. The calculations show that, for all the magnitudes studied here, the calculated values depend on the type of the exchange–correlation functionals considered in the calculation. However, for a given type of functionals, the values obtained by using pseudopotentials of type USPP and those obtained by using pseudopotentials of type PAW are almost identical. In general, the results obtained by using pseudopotentials of types USPP and PAW are more satisfactory than those obtained using pseudopotentials of type NCPP, particularly for spontaneous polarization, energy band gap and refractive indices. However, it was found that the best values for these magnitudes, i.e. those with the smallest deviation from the corresponding measured values, were obtained by using exchange–correlation functionals of types HCTH and OLYP and pseudopotentials of types USPP and PAW. Finally, the study of the spectra of optical magnitudes shows that lithium niobate in its ferroelectric phase presents interesting absorption characteristics in the ultraviolet region of the spectrum, which make it suitable for use in the manufacture of ultraviolet detectors useful for several technological applications.