[Pw_forum] ionic temperature in CP

[Nicola Marzari]

On 13/04/2013 11:45, Jin Qu wrote:
> Hi All
>
> I am a new user of cp module and I have some questions about running a
> CPMD simulation and using cppp.x.
>
> 1. I tried to run a CPMD job with 33 water molecules in a 1*1*1 nm3 box.
> After minimizing the electrons and ions to their ground states, I
> started 'verlet' dynamics as mentioned in QE user guide, without setting
> tempw ,fnosep and ion_temperature. The tempp value (ionic temperature)
> directly went up to more than 4000 and continued increasing. Did that
> make sense? Shall I turn on temperature controlling at the same time I
> started verlet dynamics? I suppose the system should oscillate around 0K
> if it has been minimized. Or is it because I started the system with a
> random molecule distribution?

In CP, typically you start the dynamics from very well converged 
electrons, but the ions are not in their eq. positions - otherwise 
nothing would move (and coupling to a thermostat atoms that do not
want to move is a very poor idea, since you pump a lot of energy in
the mode/modes that resonate with the thermostat).

The fact that your ions want to move a lot after you have relaxed them 
means that you have not relaxed them (or have not relaxed the electrons).

Have a look at the ab-intio MD video lectures and tutorial from the
UIUC school to learn more: http://www.mcc.uiuc.edu/summerschool/2006/

A lot of material here, as well: 
http://www.quantum-espresso.org/?page_id=42 , including the UCSB summer 
school, or our MIT lectures.
>
> 2. I have defined atom species as:
>
>    atomic_number(1) = 1,
>    atomic_number(2) = 8,
>
> in cppp input file.However in all generated files (out/axsf/pdb) all the
> atoms are still recognized as 'H'. What should I do with that?

Not sure - is it only for cppp? Or also for cp? It might be an incorrect
cp input file.

Please do not post again before having carefully looked at the lectures, 
tutorials, and studied your input files and run successfully some of the 
examples distributed with the code, and made sure you understood them.


				nicola


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Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL