`Structural and Electronic Properties of Expanded Selenium in the Liquid-Vapor Supercritical Region'
H.Ohtani, T.Yamaguchi and F.Yonezawa
Journal of Physical Society of Japan 67(8) 2807 (1998)
The purpose of this work is to give a theoretical explanation
of the nonmetal-to-metal (NM-to-M) transition observed in liquid
Se when the system is expanded by increasing temperature
in the liquid-vapor supercritical region.
The NM-to-M transition accompanying the expansion of the system is
unexpected since it is in contradiction to the established understanding
of NM-to-M transitions.
We introduce structural models for expanded Se and calculate
the electronic states and the wave functions of these models
by the simulated annealing method.
From the results of our calculations, we show that, when some of Se-Se
bonds are weakened in the process of
expanding the system or equivalently
in the process
of decreasing the density, the splitting
between the bonding and anti-bonding level is reduced and consequently
the anti-bonding band is relatively lowered,
which leads to the disappearance of the
band gap between the anti-bonding and lone-pair band,
or in other words
to the occurrence of the NM-to-M transition.
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