[ase-users] VASP module in ASE

[Jonas Björk]

Hi Chaitanya,


On Mon, 2008-09-01 at 22:55 +0200, Chaitanya Krishna wrote:
> Hi Jonas,
> 
> Sometimes you can also have the tag Selective Dynamics on the 7th line
> of the POSCAR. Hope you take care to check about this tag. I still
> haven't gone through the code. :P

Thank you, yes we need to think about this tag. My idea is the
following:

In a standard case where the ionic relaxation/molecular
dynamics/vibrational study/etc... is taken care by ASE, Vasp does not
need to know about the constraints since only several statics
calculations will be done in Vasp and ionic positions are updated by
ASE. This makes it possible to make use of the more flexible constraints
which ASE offers. 

However, if the user prefer to let Vasp deal with the ionic relaxation
or molecular dynamics (for example by setting ibrion=2 and nsw>0) the
constraints should be written out explicitly to the POSCAR file, so
should the initial velocities (which I totally forgot about). 


Jonas





> 
> Snip from VASP manual:
> >>>
> This file contains the lattice geometry and the ionic positions,
> optionally also starting velocities and predictor-corrector
> coordinates for a MD-run. The usual format is:
> 
> Cubic BN
>    3.57
>  0.0 0.5 0.5
>  0.5 0.0 0.5
>  0.5 0.5 0.0
>    1 1
> Selective dynamics
> Cartesian
>  0.00 0.00 0.00 T T F
>  0.25 0.25 0.25 F F F
> Cartesian
>  0.01 0.01 0.01
>  0.00 0.00 0.00
> <<<
> 
> Cheers,
> Chaitanya.