The semiconductor-metal transition in fluid selenium: an ab initio molecular-dynamics simulation

The semiconductor-metal transition in fluid selenium is investigated by means of an ab initio molecular-dynamics simulation using the generalized-gradient-corrected density functional theory. It is found that the chain-like structure persists even in the metallic state, although the chain structure is substantially disrupted. The average chain length decreases with increasing temperature, in agreement with the experimentally observed tendency. The detailed investigation of the time change of the chain structure shows that the interaction between the Se chains is crucially important for bond breaking, and that bond breaking and rearrangement of the Se chains occur more frequently at higher temperatures. It is important to note that when the Se-Se bonds break, the anti-bonding states above the Fermi level (EF) are stabilized while the bonding or non-bonding states below the EF become unstable, and, therefore, the gap at EF disappears at high temperatures.