[Pw_forum] Relaxation of low symmetry lattices

[Duy Le]

Is your question "Why do you get non-zero force for this fcc system with
your given Cell_parameters and Atomic_positions?"

If you have a perfect fcc Cu structure, you should get 0 force. I think
there are some numerical errors, it likes <<<2*0.5*6.81650937063832
.NE.6.81650937063832>>>. This kind of error "moves" the atoms off their
ideal positions. I guess if you use crystal coordinate instead of Cartesian
coordinate, you will get 0 force.

It's just my humble thought, I don't know for sure how pwscf read and
process your coordinates.

--------------------------------------------------
Duy Le
PhD Student
Department of Physics
University of Central Florida.


On Wed, Oct 7, 2009 at 5:23 PM, Manoj Srivastava <manoj at phys.ufl.edu> wrote:

> ATOMIC_POSITIONS
>  Cu  0.0   0.0   0.0
>  Cu  0.5   0.5   0.0
>  Cu  0.0   1.0   0.0
>  Cu  1.0   1.0   0.0
>  Cu  0.5   1.5   0.0
>
> K_POINTS (automatic)
> 8 8 8 0 0 0
> CELL_PARAMETERS {cubic}
>  1.5   0.5  0.0
> -0.5   1.5  0.0
>  0.0   0.5  0.5
>
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