First principles study of structural, bonding and vibrational properties of PtCoO2, PdCoO2 and PdRhO2 metallic delafossites Original Research Article

Using first principles approach, we present the structural, bonding and vibrational properties of PtCoO2, PdCoO2 and PdRhO2 metallic delafossites. The calculations have been carried out within the density functional theory and linear response formalism using ultrasoft pseudopotentials and a plane wave basis. Structural properties calculated using local density approximation (LDA) and generalized gradient approximation (GGA) to exchange correlation energy functional are found to be in good agreement with experimental results except bulk modulus, Bo, which lies above and below the experimental one, calculated using LDA and GGA respectively. Pressure evolution of oxygen internal parameter and axial ratio has been studied upto 20 GPa. Studied metallic oxides have been found to be less compressible than insulating delafossites. Density of states along with orbital contributions has been calculated to study the bonding, qualitatively. Full set of zone center frequencies has been presented. Calculated Raman active modes, A1g and Eg in these ternary oxides are found to be in excellent agreement with experimental results. Pressure coefficients and mode Grüneisen parameters have been calculated along with the variations of Raman and IR active modes with pressure.