[CP2K:5115] Re: Equipartition and calculation of vibrational, rotational and translational Temperatures

[Carlos Campana]

Why would you expect equipartition to hold in a non-equilibrium system? If
one cannot define the partition function, how are quantity averages to be
computed? Might be different when the non-equilibrium system achieves a
certain steady-state...
These are my 2 cents (haven't dusted my stat mech in a long time...)
Carlos


On Thu, Mar 27, 2014 at 3:06 PM, Rasoul Nasiri <nasir... at gmail.com> wrote:

> Hello Matt,
>
> Many thanks.
>
> I think even using NVE, one will be dealt with some errors in
> non-equilibrium situations. Could anybody please comment on it?
>
> Probably the reason is related to <mv2> = KBT in vibrational modes.
>
> Best,
> Rasoul
>
>
> On Thu, Mar 27, 2014 at 7:23 PM, Matt W <MattWa... at gmail.com> wrote:
>
>> Hi, interesting question, and I'd hope of interest to a few.
>>
>> I can't give a proper answer, but I think, in general, if you are not in
>> equilibrium, equipartition is going to break - waving hands:
>>
>> (i) you can't define your modes properly.
>> (ii) Also, most (all?, maybe some Langevin types recently implemented
>> might escape this) thermostats only work at equilibrium too, so you'd be
>> running NVE or similar where temperature isn't defined properly for a small
>> cluster.
>>
>> I guess there are tricks for steady-state thermostatted non-equilibrium
>> processes, but that is well beyond anything I know about.
>>
>> Matt
>>
>>
>> On Thursday, March 27, 2014 10:16:07 AM UTC, Rasoul wrote:
>>>
>>> Dear All,
>>>
>>> Apologize if my question seems to be irrelevant for CP2K users.
>>>
>>> I'm trying to do a non-equilibrium MD simulation using CP2K in which one
>>> molecule attacking the nano-droplet.
>>>
>>> My question is whether the equipartition of kinetic energy is satisfied
>>> in the code for vibrational, rotational and translational modes at high
>>> temperatures and non-equilibrium situations?
>>> Having said this if <mv2> = KBT works properly for estimation of
>>> temperature in the vibrational modes even using small time steps?
>>>
>>> Many thanks,
>>>
>>> Best,
>>> Rasoul
>>>
>>>
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