Structural stability of thallium-V compounds

We have performed ab initio self- consistent calculations in order to investigate the structural stability of the thallium - V compounds: TlN, TlP, TlAs, TlSb and TlBi. Total energy calculations of several phases are considered here in order to fix the most stable structure for each compound. For the structures considered, the wurtzite one is found to be the ground state phase for TlN, the zinc- blende phase that for TlP and TlAs, while TlSb and TlBi favour the tetragonal PbO phase. Some unusual features, compared with the other III - V families, are registered for the systems studied, which we attempt to analyse and to explain in detail in the present paper.