[Pw_forum] a possible problem in the routine add_efield.f90

[Paolo Giannozzi]

On Nov 16, 2008, at 7:27 , hanghui chen wrote:

> The additional force is calculated by the routine add_efield.f90.
> However in routine add_efield.f90, it only calculates the magnitude
> of the force but does not specify the direction (the additional force
> only has one direction).  Therefore all the forces in the 'reversed
> region' are not correctly calculated because the direction of  
> 'forcefield'
> is NOT reversed as is the external electric field.

I think the sawtooth potential was meant to reproduce the case of a
homogeneous electric field on a slab. The sawtooth potential is supposed
to reverse in the vacuum region and to yield a constant electric  
field in the
region where atoms are. An electric field reversing in the middle of  
the layers
was not considered a physical case, I guess. Of course this  
limitation should
be documented, or else the unexpected placement of the reversal should
produce an error, or else this case should be implemented (assuming  
it has
any physical interest, which is far from obvious to me).

Paolo
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222