Dear Rui,
On 12 Aug, 2011, at 16:12, DONG Rui wrote:
> Hi, all,
>
> I am doing MD calculation in QuantumEspresso, and have a question now...
>
> here are some of the input list
> &ions
> ion_temperature = 'reduce-T',
> tempw=10,
> delta_t = 1,
> nraise=10,
> pot_extrapolation='second-order',
> wfc_extrapolation='second-order',
> /
>
> But I found the rescaling works only when delta_t is a negative number, which
> is different from what the documentation tells me.
In Doc/INPUT_PW.txt, I find the following lines:
Variable: ion_temperature
Type: CHARACTER
'reduce-T' reduce ionic temperature
every "nraise" steps
by the (negative) value "delta_t"
and
Variable: delta_t
Type: REAL
if ion_temperature='reduce-T':
every 'nraise' steps the instantaneous temperature
is
reduced by -delta_T (.e. delta_t is added to the
temperature)
The instantaneous temperature is calculated at the end of
every ionic move and BEFORE rescaling. This is the
temperature
reported in the main output.
For delta_t < 0, the actual average rate of heating or
cooling
should be roughly C*delta_t/(nraise*dt) (C=1 for an
ideal gas, C=0.5 for a harmonic solid, theorem of energy
equipartition between all quadratic degrees of freedom).
Why delta_t is a negative number is different from the document?
>
> Anyone has the same problem? And does anyone know how to heat the system up
> use the method "reduce-T"?
I think "reduce-T" is used to quench the system, it reduces ionic temperature
every "nraise" steps by the (negative) value "delta_t".
To heat the system up, I would suggest you to use other thermostats, like
"rescaling", "rescale-v", "rescale-T", "berendsen" or "andersen".
Best wishes,
Changru
>
> Thank you guys!
>
> Rui _______________________________________________
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> Pw_forum at pwscf.org
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---
Changru Ma
SISSA & Theory at Elettra group
email: crma at sissa.it
tel: +39 040 378 7870
http://www.sissa.it/~crma
---
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