AB-INITIO PSEUDOPOTENTIAL STUDY OF THE STRUCTURAL PHASE-TRANSFORMATIONS OF ZNS UNDER HIGH-PRESSURE

Using a first-principles pseudopotential approach and the local-densit y approximation for the exchange-correlation potential, we have calcul ated the equations of state (EOS's) of the zinc-blende (ZB), rocksalt (RS), beta-Sn, and cinnabar structures of ZnS. From these EOS's the hi gh-pressure structural phase transformations (HP-SPT's) of ZnS were in vestigated. These calculations were performed using two approximations for treating the semicore 3d electrons of Zn: as relaxed valence stat es, and as part of the frozen core and using nonlinear exchange-correl ation core corrections (NLCC). It has been found that the NLCC calcula tions provide a very good description of the structural parameters and the HP-SPT's of ZnS, provided that the Zn pseudopotential is generate d from nonrelativistic atomic calculations. The cinnabar structure is found to be an intermediate phase between the ZB and the RS structures of ZnS, a behavior which was previously associated only with the Te- and Hg-based II-VI compounds. The structural parameters of the cinnaba r form of ZnS have very similar behaviors as those of the same structu re of HgTe and CdTe.