The ABINIT Users Mailing List ( CLOSED )

[Clovis Darrigan <clovis.darrigan@univ-pau.fr>]

> - The tutorial example describes how to calculate the phonon modes in a
> perturbation using an electric field. I would like to calculate the
> atomic displacements as a result of the application of the electric
> field, i.e. the resultant structure in addition to the phonons.

Hello,

To do this, the electric field must be present during self-consistent calculation, allowing atoms to relax in the field, but screened by local field.

If the response function due to the electric perturbation is well implemented in ABINIT, I think that homogeneous electric field cannot be used during calculation of ground states wavefunction, and so not relaxation of atoms. CRYSTAL2003 code, for example, contains this electric field in hamiltonian, and you can choose the value of intensity [1] (but of course, this code has not the same theoretical basis than ABINIT).

Another problem is that an homogeneous electric field cannot be applied in a triperiodic structure because of boudary conditions. In general we use a triangular electric potential (as a sawtooth) in big supercells along the direction of field. In this cas, the triangular potential is periodic [2]. This is more simple in the case of a slab if you want the field perpendicular to the slab surface (in this case, as there is no translation symmetry in this direction, field can be described linearly). But this is for CRYSTAL and not yet (?) for ABINIT.

[1] Implementation of the finite field perturbation  method in the CRYSTAL program for calculating the  dielectric constant of periodic systems, C. Darrigan, M. Rérat, G. Mallia,  R. Dovesi, Journal of Computational Chemistry, 24, 11, p. 1305 (2003)
[2] Ab initio calculation of the macroscopic dielectric constant in silicon, S. Baroni, R. Resta, Phys. Rev. B, 1986, 33, 10, p. 7017

Sincerely,
<x-tad-smaller>_________________________________________________________________________
Dr. Clovis Darrigan
Maitre de Conferences

Laboratoire de Chimie Structurale, UMR5624
University of Pau and Adour Countries
IFR rue Jules Ferry, 3e etage
BP 27540, 64075 Pau cedex
Phone +33 559 40 78 59 - Fax +33 559 40 78 62
http://www.univ-pau.fr/umr5624/
_________________________________________________________________________
Web sites: http://www.univ-pau.fr/~darrigan/</x-tad-smaller>