[Pw_forum] heating and cooling vc-md

[Jalil Mahdizadeh]

Thank you for your precious tips. I will try with lammps that I'm a little
expert on.

------------------------------------------
S. J. Mahdizadeh

On Oct 23, 2017 11:00 PM, "Axel Kohlmeyer" <akohlmey at gmail.com> wrote:

>
>
> 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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>>>>
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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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