[Wien] Electric dipolar moment

[Fred Nastos]

On September 29, 2005 06:46 am, Victor Pardo Castro wrote:
> does anybody know if it is possible to calculate the electric dipolar
> moment of the unit cell within WIEN2k?.

Since no one has answered this...

Consider a one-dimensional crystal made up of a row of point charges
equally spaced by a distance d.  The charges all have equal magnitude, Q,
but alternating signs.  Let's schematically represent the crystal like:

	... + - + - + - + - + - + - ...

What is the unit cell?  And what is its electric dipole moment?

As usual we have different choices to defining the unit cell.
One choice of unit cell is

		- +

This choice of unit cell leads to a dipole moment Qd to the right.
Instead, we could have equivalently chosen the unit cell to be

		+ -

For this choice of unit cell the dipole moment is Qd to the left.

See the problem?  It has caused some sleepless nights.

Cheers,

Fred