Relative stability of ThAl2 and ThGa2 under high pressure

ThAl2 and ThGa2 exhibit quite different structural and compressibility behaviour under pressure: whereas ThAl2 undergoes a series of structural transitions under pressure up to 30 GPa, ThGa2 remains stable up to 62 GPa. The relative structural stability of ThAl2 and ThGa2 have been compared and contrasted in terms of their electronic structure at different pressures. Their electronic structure calculations were carried out using the Full Potential Linear Augmented Plane Wave (FP-LAPW) method with spin-orbit interaction as a function of reduced volume. In ThAl2 the f-bands lie about 2.5 eV above Fermi level (EF) and are populated with mostly the dp hybridised states. The EF lies on a shallow valley with very low density of states (DOS). In ThGa2 also, the f-bands lie about 2.3 eV above EF, but the EF lies on a steep valley with very low DOS. However, on closer examination the change in the density of states on the bonding and antibonding sides of the Fermi level seems to be much steeper than that in ThAl2. Further, the computations for reduced volume revealed that the bands around EF and hence the density of states in both the systems responded very differently to pressure. This is discussed in the context of their structural stability under pressure.