[Pw_forum] Cannot reach the target temperature in vc-md calculation using pwscf; and where I can find the updated velocities?

[Davide Ceresoli]

Dear Tian,
     I'm experiencing the same problem, also in 5.0.2. I think that the
default choice of the cell mass is not appropriate. The kinetic energy of the
cell d.o.f. is added to the ions kinetic energy, then velocities are
rescaled. If ionic temperature is always smaller than tempw, it might be
that the cell d.o.f. suck a consistent fraction of the ionic temperature.
I'm not 100% sure about that. I will perform some test by reducing wmass,
then I'll report the outcome.
I've also reported this problem to QE developers mailing list, and I'm
waiting for suggestions.

HTH.

Best wishes,
     Davide


On 11/30/2012 09:49 PM, Tian Lan wrote:
> Thanks. I want to use vc-md, because it is NPT enemble. I would like to see the
> cell response to temperatures, e.g. . I did not find any explicit comment about
> the bug of temperature control. But I did see one recent message saying a very
> similar problem. So at this point, I am not sure whether the problem comes from
> the setup or from the code itself.
> What I do see is the control commands are not effective at all. The tolp=10 and
> tolp=100 almost have the same output, e.g., which is disappointing. When
> tempw=100K, it did converge well, but tempw=300K can only reach 200K. And, a
> smaller cell seems to perform worse in temperature control. So there are a lot
> of phenomena. If someone is familar with this, or knows the relationship between
> those seemingly messy observations, please let me know. Or it is indeed the code
> problem, I will try to use another one. Thanks a lot !
> Tian
>