Electronic properties ofNb3Ge andNb3Al from self-consistent pseudopotentials. II. Bonding, electronic charge distributions, and structural transformation

Electron charge distributions are presented for ${\mathrm{Nb}}_3$Ge, ${\mathrm{Nb}}_3$Al, and two hypothetical $A-15\mathrm{}$ structures. Results indicate that the bonding in these materials is mainly metallic in character with some covalentlike bonding between Nb-chain atoms. We find significant coupling between neighboring chains and also between chain atoms and atoms at the cubic site. Comparison is made with various theoretical models. Investigation of the charge character of states near $E_F$ suggests further developments in current theories on the structural transformation of $A-15\mathrm{}$ compounds. The effect of chain dimerization on electronic states and charge distribution of ${\mathrm{Nb}}_3$Ge is also investigated.