Theoretical analysis of structural stability of TM5Si3 transition metal silicides

A combination of electronic-structure calculations from density-functional theory (DFT) through a tight-binding (TB) model to analytic bond-order potentials (BOPs) has been used to investigate the structural trend of the TM₅Si₃ compounds across the early transition metals (TM). First of all, the formation energies of TM₅Si₃ , whose ground states adopt the competing D8₈ , D8_l , or D8_m structure types, have been calculated by using DFT (TM is Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, or W). In agreement with experiments the DFT results predict the observed D8₈→D8_m structural trend across the 3d series and the D8₈→D8_l→D8_m trend across the 4d and 5d series. A p-d canonical TB model is then shown to reproduce these trends, thereby providing a valid basis for the application of BOP theory. By performing a moment analysis within the BOP formalism, we conclude that up to the fifth moment of the density of states is required to explain the structural trend across the 3d series whereas up to the ninth moment is required for the 4d and 5d series.