[Pw_forum] 'Relax' variable

[Lorenzo Paulatto]

On Wed, 10 Mar 2010 13:03:05 +0100, Masoud Nahali <masoudnahali at live.com>  
wrote:
> 1. fixing or changing the cell symmetry  through the calculation.

Stress and force components that would break the symmetry are always  
zero... by symmetry

> 2. fixing or optimizing the cell size through the calculation.

Just use relax instead of vc-relax, if you mean the *volume* of the cell,  
than there is a keyword for that but unluckily it does not work very well  
with bfgs...

> 3. optimizing all positions without considering any restrictions.

This is the default, however you can fix the position of one or more atoms  
along any cartesian direction if you wish.

best regards

-- 
Lorenzo Paulatto

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