`Nonmetal-Metal Transitions of Expanded and Compressed Selenium
near the Liquid-vapor Critical Point and under High Pressure'
H.Ohtani, T.Yamaguchi and F.Yonezawa
Progress of Theoretical Physics Supplement 138 247 (2000).
The structural and electronic properties
of expanded and compressed Se
due to its volume expansion and compression
are investigated by the density functional method.
The volume expansion breaks Se chains
and the energy of anti-bonding ($\widetilde{\sigma}^{\ast}$) bands
corresponding to the broken bonds reduces,
which induces a nonmetal-to-metal (NM-to-M) transition.
The volume compression,
on the other hand, increases
the band width and the system
transforms from NM to M phase.
When the system has structural disorder,
the energy of the $\widetilde{\sigma}^{\ast}$,
which correspond to the long bonds, is decreased.
This situation induces
an NM-to-M transition
in liquid Se under compression at a pressure
lower than that for crystalline Se.
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2000/10/12