[Thermo_pw-forum] thermo_pw

[Andrea Dal Corso]

Presently no. There is no way neither to impose a finite pressure nor  
to do the calculation with a finite stress.

Andrea



Quoting Suza W <suza.rri at gmail.com>:

> Hi Andrea,
>
> Thank you very much for your kind reply.
> I see that Example 9, can compute  average Gruneisen
> parameters for an equilibrium geometry. Using thermo_pw code,
> is it possible to compute the same for a structure expanded (under
> stressed) uniformly
> (tri-axially keeping the same cubic symmetry) or biaxially ?
>
> Suza
>
>
> *P.S.  Awaiting moderator approval, next time going to use the mailing list
> Thermo_pw-forum.*
>
> On Wed, Jan 28, 2015 at 4:08 PM, Andrea Dal Corso <dalcorso at sissa.it> wrote:
>
>> There are two reasons the two curves are different. One because the
>> numerical parameters are not well converged. Typically one needs more k
>> points, or the delta_t of temperature is not small (or big enough), or
>> you need more geometries. The other is that the two procedures are
>> different. At high temperature the quasi-harmonic approximation fails
>> and the two curves start to differ. At very low temperatures the
>> derivative of the lattice constant is not accurate because the changes
>> of lattice constants are quite small, so in that case the calculation
>> with Gruneisen parameters should be more accurate. I think the two
>> curves give you an idea of how much you can trust the calculated thermal
>> expansion.
>> The example is not completely converged, otherwise it would require too
>> much time to finish.
>>
>>
>> Andrea
>>