The infrared spectrum of spessartine : An ab initio all electron simulation with five different functionals (LDA, PBE, PBESOL, B3LYP and PBE0)

The performance of five different density functionals (LDA, PBE, PBESOL, B3LYP and PBE0) in describing the infrared spectrum of a crystalline periodic system with a large unit cell (spessartine, 80 atoms in the primitive cell) is studied by using the periodic ab initio Crystal09 code and an all electron basis set. The transverse (TO) and longitudinal (LO) optical branches of the 17 IR active modes are evaluated together with the oscillator strengths and the high frequency dielectric tensor ϵ ∞ . These ingredients permit to compute the dielectric function ϵ ( ν ) , and then the reflectance spectrum R ( ν ) , which is compared with experiment.