First-principles calculations of liquid CdTe at temperatures above and below the melting point

We perform ab initio molecular-dynamics simulations of CdTe at three differ ent temperatures: 800 K (supercooled state), 1370 K (near the melting tempe rature), and 3000 It (superheated state). In agreement with experiment, we find that upon the melting, CdTe experiences a semiconductor-->semiconducto r transition. In its liquid state, CdTe retains its tetrahedral environment with the coordination number similar to 4. We find that heating CdTe much above its melting point leads to substantial structural changes with a tran sformation to a more close-packed atomic structure. The coordination number of the superheated phase is similar to 6 and the de electrical conductivit y is an order of magnitude larger than at the melting temperature. This, al ong with the disappearance of the finite band gap, suggests a gradual semic onductor-->metal transition in the CdTe system at a temperature higher than melting point. We also find in liquid CdTe, near the melting temperature, atoms of Te form infinite branched chains. Short and simplified chains are still present in the supercooled phase. As the temperature increases, chain s break, become shorter, and, eventually, transform to form close-packed cl usters in the supeheated state. We also examine dynamical and electronic pr operties of the CdTe system.