  In this study, using the density functional theory, we have investigated the
bulk physical properties like structural, electronic band structure, elastic
properties, thermal properties, optical properties and bonding features of
AlPO4 compound in the hexagonal form. The values of our optimized structural
parameters are very close to the previous results. Most of the results
presented in this work are novel. The elastic constants indicate that AlPO4 is
mechanically stable and brittle in nature. The compound is moderately hard and
possesses low machinability index. AlPO4 contains significant elastic
anisotropy. The charge density distribution , bond population analysis, Vickers
hardness, thermo-mechanical properties, and optical properties have been
investigated for the first time. The electronic band structure calculations
reveal clear insulating behavior with a band gap of 6.0 eV. Band structure
calculations were carried out without and with spin-orbit coupling (SOC) to
explore possible topological signature. The energy dependent optical properties
conform to the electronic band structure calculations. Major optical properties
like dielectric functions, refractive index, photoconductivity, absorption
coefficient, loss function and reflectivity are calculated and discussed in
detail in this study. The compound is optically anisotropic. It is an efficient
absorber and reflector of the ultraviolet light.
