[Pw_forum] heating and cooling vc-md

[Axel Kohlmeyer]

On Mon, Oct 23, 2017 at 3:04 PM, Jalil Mahdizadeh <saja.mahdizadeh at gmail.com
> wrote:

> What we were discusting about (solid-solid phase transition probably).
>

​well, it depends on the specifics of the system, and whether reaxff is
applicable depends on whether there is a suitable and suitably reliable
parameter set.
nobody but yourself or somebody working on the same kind of problem can
make a definite statement. you'll have to carefully study the literature,
make tests and benchmarks and also study the thermodynamics of the
processes that you are modeling. none of that is specific to QE, either.
i've told you about as much as somebody with a general stat mech and MD
background can tell you.

axel.​



> ------------------------------------------
> S. J. Mahdizadeh
>
> On Oct 23, 2017 10:29 PM, "Axel Kohlmeyer" <akohlmey at gmail.com> wrote:
>
>
>
> 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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>>
>>
>> --
>> 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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-- 
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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