`Nonmetal-metal Transition in Expanded Selenium by the Spin Density Functional Method'
H.Ohtani, T.Yamaguchi and F.Yonezawa
Journal of Physical Society of Japan 69(12) 3885 (2000).
The purpose of this paper is to
investigate the electronic properties of
expanded selenium (Se) near the liquid-vapor critical point
by the spin density functional (SDF) method
as well as by the density functional (DF) method
both with
the local density approximation (LDA)
and the generalized gradient approximation (GGA).
In any case of the four possible sets
(DF+LDA, SDF+LDA, DF+GGA and SDF+GGA),
our results show that,
when some of Se-Se bonds are broken
in the process of expanding the system,
(1)
the bonding levels go upward
while the unti-bonding levels go downward
for the weakened bonds, and then
the energy difference between them is decreased,
(2)
the energetically smallest states become relatively lowered
from the conduction anti-bonding bands,
and then the anti-bonding states overlap with
the valence lone-pair band,
(3)
expanded Se finally transforms from a nonmetal to a metal.
In this metallic state,
the local three-fold structure is formed
between the terminal atom of the chain and the neighbour chain.
When the system is expanded furthermore,
the band width becomes reduced
and the spin polarization takes place at the terminal atom of the chain.
Further expanded Se transforms to a nonmetal.
In the volume region of our interest,
the calculated energy levels are the same
for any of these four sets.
Consequently, the mechanism we have proposed for
nonmetal-to-metal transition of expanded Se remains intact
even when the calculations are carried out in different methods.
Back
2000/12/07