[CPMD-list] Timestep problem

[Lukasz Walewski]

Dear Ari,

On Sat, May 14, 2005 at 04:14:37PM +0200, Ari P Seitsonen wrote:
> 
> Dear Younes,
> 
> On Sat, 14 May 2005, Younes Ansari wrote:
> 
> >I want to know if there is anyway to increase the timestep to 1000
> >without getting any NANs or without any big physical changes.
> 
> 1000???? That's certainly impossible: The atomic motion is already much
> faster than what your period would be. As kind of rule-of-thumb the time
> step in classical or Born-Oppenheimer molecular dynamics has to be at most
> 1/6th .. 1/10th of the highest ionic vibration. In addition in
> Car-Parrinello dynamics the time step is even smaller because the
> electronic motion must average out during the ionic vibrations. And if

Wouldn't it be nice to integrate the electronic degrees of freedom with
sufficiently small time step and the ionic movements with a bit larger one ?

I know the TIMESTEP ELECTRONS and TIMESTEP IONS options but had some
trouble using them. Could you please give some advise on setting different
time step for the electronic and the ionic motions ?

With best regards,
Lukasz


-- 
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Łukasz Walewski <ljw at icm.edu.pl>