[Pw_forum] vc-relax

[Lorenzo Paulatto]

On Wed, July 8, 2009 11:03, ali kazempour wrote:
>  Can I use vc-relax to optimize the value of lattice constant in ZnO
>  wurtzite structure?

Dear ali,
of course you can!


> Because the lattice constant change and also atomic
>  positions either.

You can nail the atoms to their position by adding " 0 0 0" after the
atomic coordinates (see manual for detail), although it only make sense
for crystal and possibly alat coordinates, when you are doing vc-relax.

> After finishing the run, Which atomic position shoud be
>  used in next calculation(relaxed position or initial positions)?

The optimized ones, if not, why would you do the optimization?

>  How can I
>  optimize the value of u that is ideally equal to 3/8?

Doing vc-relax, I don't see the problem )I asume you are using this
notation: http://cst-www.nrl.navy.mil/lattice/struk/b4.html). If you want
the Zn atoms to stay in z=0 you can fix their position as explained above;
nevertheless "u" is just the difference in the z coordinate of Zn and O
atoms.

>  thanks a lot

you are welcome, best regards


-- 
Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/



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