The eigenvalue problem is described as,
|
(3.19) |
where
and
are an eigenvalue
and an eigenvector of this problem, respectively. The coordinate
system is Cartesian. The
is called
polarization vector which corresponds to the normalized atomic
displacements weighted by the square root of the atomic mass as
written by,
|
(3.20) |
where
is the amplitude vector of an atomic displacement.
The corresponds to vibrational frequency. The
is complex number and the phase factor at
given instant is expressed by
. The normalization is expressed
as,
|
(3.21) |
The normalized atomic displacement is obtained by,
|
(3.22) |
The origin where the radial vector is measured can be set at an
arbitrary point in the real space. An eigenvector calculated at an
exact k-point can be represented by the atomic modulations in the
calculated supercell at an arbitrary instance . However the
amplitude of the displacements is not described by
Eq. (3.24), but is calculated by the
thermodynamic properties.
togo
2009-02-12