Valence of pnictides and chalcogenides

At ambient conditions, the lanthanide monopnictides RX (X = N, P, As, Sb, Bi) and monochalcogenides RX (X = 0, S, Se, Te, Po) crystallize in the NaCl structure. Given the combination of an electropositive R-ion with an electronegative pnic-tide or chalcogenide, one might assume that an ionic picture can be applied here. But based on the observed properties, Rhyne and McGuire (1972) proposed a classification distinguishing between the so-called valence balanced compoimds 

Pnictide R , Chalcogenide R, and valence imbalanced compounds such as 

Chalcogenide R . The former being mostly ionic insulators, although there are exceptions, and the latter being mostly conductors. 

In Table 2, we show the spin-resolved band gaps and densities of states of each material at the Fermi energy. It is clear from the table that our SIC-LSD 

FIGURE 7 Total energy differences (in eV) between divalent and trivalent scenarios for lanthanide nitrides (triangles). The results for elemental lanthanides (diamonds) are repeated for an easy comparison (including 43 mRy correction, but not for the nitrides). 

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