[Pw_forum] heating and cooling vc-md

[Axel Kohlmeyer]

On Mon, Oct 23, 2017 at 2:31 PM, Jalil Mahdizadeh <saja.mahdizadeh at gmail.com
> wrote:

> Thanks god. I was thinking  I'm some kind of hollow man nobody can see me.
> However, dear axel recently a group of magicians accomplished such a
> "doomed project" successfully.
>
​please note that you asked about "phase transition" without any particular
detail of what kind of transition you are after. in the most general case
one would assume a solid-liquid or liquid-gas transition. those are
activated processes with a significant barrier and all the issues i
mentioned. in fact, if somebody is after determining a melting point or
similar this way, even classical MD will fail.

if you look at the transition in the paper you quote, it is a solid-solid
transition with rather minimal changes to the geometry and probably a very
small activation barrier, if any. yet, those folks still used a very large
supercell.​ that is quite telling.

at any rate, my statement, that any temperature increase will be "rapid"
for AIMD simulations still stands.

​axel.​




> PHYSICAL REVIEW B 96, 054111 (2017).
> ------------------------------------------
> S. J. Mahdizadeh
>
> On Oct 23, 2017 9:16 PM, "Axel Kohlmeyer" <akohlmey at gmail.com> wrote:
>
>>
>>
>> On Mon, Oct 23, 2017 at 1:04 PM, Jalil Mahdizadeh <
>> saja.mahdizadeh at gmail.com> wrote:
>>
>>> Dear QE users,
>>>>
>>>> I'm going to perform some vc-md with gradually heating/cooling process
>>>> until achieving phase transition temperature. Does any body know how to do
>>>> heating/cooling process in vc-md? I know that only "rescaling" option is
>>>> implemented for vc-md. Could Nobody help me?
>>>>
>>>
>> ​i suppose nobody has replied, because nobody wanted to tell you that
>> what you are asking about, is a doomed project.
>>
>> at the time scales accessible to DFT based MD simulation, heating/cooling
>> will *always* be rapid.
>> also, it is a good idea to stay away from phase transition temperatures​,
>> since there you will have very bad sampling of phase space and suffer from
>> massive finite size effects.
>>
>> ​axel.​
>>
>>
>>
>>>
>>>> Cheers.
>>>>
>>>> ‌
>>>>
>>>
>>>
>>>
>>> --
>>> S. J. Mahdizadeh
>>>
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>>
>>
>>
>> --
>> Dr. Axel Kohlmeyer  akohlmey at gmail.com  http://goo.gl/1wk0
>> College of Science & Technology, Temple University, Philadelphia PA, USA
>> International Centre for Theoretical Physics, Trieste. Italy.
>>
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>
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-- 
Dr. Axel Kohlmeyer  akohlmey at gmail.com  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.
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