[Pw_forum] heating and cooling vc-md

[Axel Kohlmeyer]

On Mon, Oct 23, 2017 at 2:58 PM, Jalil Mahdizadeh <saja.mahdizadeh at gmail.com
> wrote:

> Thank you Axel. Hence, I'm thinking about ReaxFF based MD instead. What do
> you think?
>

​using reaxff to do what?

axel.​



> ------------------------------------------
> S. J. Mahdizadeh
>
> On Oct 23, 2017 10:21 PM, "Axel Kohlmeyer" <akohlmey at gmail.com> wrote:
>
>
>
> 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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-- 
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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