[Pw_forum] Stress calculation in quantum espresso

[Paolo Giannozzi]

On Jul 1, 2009, at 16:49 , Lorenzo Paulatto wrote:

>> (2) pot | wfc_extrapolation
>>  please clarify if 'first_order', 'second_order' can be used in
>> calculations  other than 'md' or 'vc-md'. I used these options in
>> 'relax' and 'vc-relax'  without any errors, too. Of course, I  
>> don't know
>> if these were really in effect.
>
> Both can be used for non-dynamical optimization (such as BFGS),  
> although
> they don't strictly make very much sense. Nevertheless, they can help
> speeding up convergence, especially when the minimization steps get
> smaller. I would need to consult Paolo Giannozzi (who implemented the
> extrapolation) to be 100% sure.

I didn't implemented the extrapolation, I just tried to clean up the  
mess that
it used to be. First- and second-order extrapolation are devised to  
work in
conjunction with a MD sequence of time steps. There is no point in using
them for structural optimization, in my opinion.

>> (3) ecfixed, qcutz and q2sigma
>>  in the original paper, the framework is an extension of PR  
>> dynamics to
>>  CP. Please clarify [...]

please experiment a little bit and report what you found

P.
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222