Electronic structure of AFe2P2, A = Ca,Sr,Ba

The compounds CaFe2P2, SrFe2P2 and BaFe2P2 crystallize in the ThCr2Si2 structure which is a ternary variant of the BaAl4 structure. In order to investigate the bonding properties, band-structure calculations using the full-potential linearized augmented plane wave (FLAPW) method have been performed. For the three compounds densities of states (DOS), local partial DOS and electron densities have been calculated. Compared to CaNi2P2 with a P-P distance of 2.30 Angstrom, a value very close to that for a P-P single bond, this distance is 2.71 Angstrom for CaFe2P2. While in the latter compound one still observes pronounced P-P(s-s and p-p) sigma-bonds, this is not the case, apart from very weak p-p interactions, for SrFe2P2 and BaFe2P2 (P-P distances: 3.43 Angstrom and 3.84 Angstrom respectively). Despite their different c/a ratios the Sr and Ba compounds show fairly similar bonding properties, in particular as far as the Fe-Fe and Fe-P interactions are concerned. In BaFe2P2, however, non-negligible interactions of the semicore [Ba(5p)] states with the P(3s) states are found. (C) 1997 Elsevier Science S.A.