Electronic structure of zintl compounds (NaTl) and alkali pnictides

The presence of both like and unlike atom nearest neighbours in the NaTl lattice is used to test the dependence of tight-binding interactions on bond type. The atoms are found to be almost neutral, and little evidence of the classic Na⁺Tl^- bonding models is found. The bands of alkali pnictides such as Li₃Sb are calculated by scaling interactions from LiAl. The Li salts are found to have almost neutral sites whereas the Cs salts are strongly ionic. We classify the bonding generally as charge transfer, not covalent.