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

[Tian Lan]

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

On Thu, Nov 29, 2012 at 9:49 PM, Tian Lan <tianlan at caltech.edu> wrote:

> Dear all,
>
> I am running vc-md of a cuprite structure with 2 by 2 by 2 supercell. When
> I set the tempw=300, it does converge but the equilibrium temperature seems
> to be only 190K. It starts from 280 and all the way down to 190K and
> converges there. Actually I did not find many controls on it, below is what
> my current setups for &ions and &cells.
>
> I kept trying different setups, but has little effect, for example, I
> tried different 'dt' from 20 to 50, different 'ion_temperature' choices,
> 'tolp' or 'nraise'. I also used a primitive cell, the actual temperature
> can be only 108K or so. Therefore, I am not sure whether it has something
> to do with the cell size, or the temperature calibration issue, or some
> setup would substantially influence the temperature control.
>
>  &ions
>     tempw=300,
>     ion_temperature= 'rescaling',
>     tolp=20,
>     nraise=1,
>     pot_extrapolation='second-order',
>     wfc_extrapolation='second-order',
>  /
>  &cell
>     cell_dynamics = 'pr' ,
>     press = 0.00
>  /
> Besides of it, I have a stupid question because I did not find any
> information about the atom velocities. I only find updated coordinates and
> forces in .out file. In .save folders, I did not find anything either. My
> control icons for print are as follows:
>
>     disk_io='high'
> !    wf_collect=.TRUE.
>     pseudo_dir = '.',
>     outdir='\temp'
>     tstress =.true.,
>     tprnfor =.true.,
>
> Thank you in advance if you have any idea about these.
> Best Regards,
> Tian
> --
> Lan, Tian
> Ph.D. Candidate, Department of Applied Physics and Materials Science
> California Institute of Technology,
> Caltech M/C 138-78, Pasadena, CA, 91125
>



-- 
Lan, Tian
Ph.D. Candidate, Department of Applied Physics and Materials Science
California Institute of Technology,
Caltech M/C 138-78, Pasadena, CA, 91125
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20121130/ab1b3eea/attachment.html>