[CPMD-list] Timestep problem

[Ari P Seitsonen]

Dear Lukasz,

   Having different time step for the electrons and ions doesn't usually
bring anything, since the propagation of the ionic degrees of freedom 
takes only a fraction of the time compared to the effort needed to 
propagate the electronic degrees of freedom. As far as I know the 
different time steps for the electrons and ions in the input for CPMD is 
meant for the QM/MM calculation, but anyone please feel free to correct 
me.

     Greetings,

        apsi

On Sat, 14 May 2005, Lukasz Walewski wrote:

> 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
>
>
>

-- 
-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari P Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
   CNRS & IMPMC, Université Pierre et Marie Curie
       4 place Jussieu, case 115 / F-75252 Paris
   Tel: +33-1-4427 7542, Fax: +33-1-4427 3785, GSM: +33-6-6736 3820