A first-principles investigation of the electronic structure and the chemical bonding for CaFe2P2 and CaNi2P2

For tetragonal CaFe2P2 and CaNi2P2 with ThCr2Si2 structure self-consistent full-potential LAPW band-structure calculations have been performed. Both compounds show metallic behavior. Bands predominantly originating from P s states are found approximately 0.8 Ry below the Fermi energy. After a gap a ca. 0.5 Ry wide region of overlapping, occupied bands is observed. The bottom part of this band complex is formed by bands originating from P p states while in the upper part bands with a high Fe or Ni d character, respectively, are dominant, An analysis of the bonding situation in the two compounds is performed in terms of local partial densities of states, partial charges, and electron density plots. The main contributions to covalent bonding are due to Fe-Fe/Ni-Ni, Fe-P/Ni-P, and P-P interactions in the respective compounds, where the latter are considerably stronger in CaNi2P2 (corresponding to the shorter P-P distances in this compound) while the opposite is true especially for the Ni-Ni bonds (first and second neighbors) as compared to the Fe-Fe bonds in CaFe2P2. Also nonnegligible covalent Ca-Ca, Ca-Fe/Ca-Ni, and Ca-P interactions are found in both compounds. (C) 1997 Academic Press.