[Pw_forum] ionic temperature in CP

[Jin Qu]

Thank you Prof Marzari and dear Antonio,  your answers are very helpful !

many thanks

Jin


2013/4/15 Antonio Tilocca <uccaati at ucl.ac.uk>

>
> >
> > 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?
>
>
> To answer your first question: yes, an initial "rocketing" ionic
> temperature is not unexpected if you start from a configuration very far
> from equilibrium, no matter how well you relax the electrons. However,
> also be aware that there can be other causes for this behaviour, such as
> an inappropriate (too long) time step, wrong cell vectors specified, etc.
> In order to rule out the latter, you can try to start from a more stable
> configuration, for instance obtained from a quick relaxation by classical
> MD. In principle you could also try to turn on damped MD to prevent ions
> from moving too fast and too much in the initial stages of the CP
> dynamics, and
> see a short damped MD run gives you a better starting configuration.
>
>
> Antonio Tilocca
> Chemistry
> University College London
>
>
>
>
>
>
>
>
>
> >
> > 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?
> >
> > many thanks
> >
> > Jin
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