[gpaw-users] LCAO mode for Zeolite

[Ask Hjorth Larsen]

Dear Baldissin

2012/7/12 baldissin <baldissin at yahoo.it>:
> Dear gpaw users
>
> I am calculating the site preference of Al substitution in zeolite.
> Unit cells are massive ( 20x20x13 Ang ). My idea is using LCAO mode.
> I am wondering if the method is accurate enough to discriminate energy
> with difference of some meV (5-20).
> any opinion?
>
> thanks a lot
> Gael
>
> PS:   calc = GPAW( mode='lcao' ,  h=0.18, nbands=-5, xc='PBE',
> txt='atoms.out', kpts=[(0, 0, 0)], usesymm=True , charge=-1,
> maxiter=150   )

Energies in LCAO mode are usually off quite significantly.  However
trends are reproduced very well in my experience.  You may need to do
it the hard way and compare to some grid-based calculations.

Be sure to follow the advice for optimizing the performance of the
Poisson solver in such a large system:
https://wiki.fysik.dtu.dk/gpaw/documentation/lcao/lcao.html#notes-on-performance

(Don't reduce the solver's tolerance, but make sure the number of grid
points is divisible with a high power of 2).

You don't need to specify kpts and usesymm above.  You will need
basis='dzp' set if you want sensible numbers though.

Regards
Ask