[CP2K-user] [CP2K:14524] How to find the global minimum...?

[Lucas Lodeiro]

Hi Monu and Fangyong,

I disagree a little bit with Fangyong because an AIMD calculation is not
cheaper, and if the barriers between local minimas are high, you cannot see
a structural change with the MD, at least in the scale time of ps. Firstly,
I would try to optimize a couple of structures and measure the energy
differences, this will give you a little insight about the barriers (the
minimum energy for the barriers), If they are high, the AIMD probably
cannot move from one local minima to another. If they are little, you can
see the structural changes, but in this case, probably the global minima is
not sufficient to modulate the properties of the system, and some other
local minima have to be taken into account.
Other way is to generate with a script random positions of the molecule
into the MOF and minimize them with a semiempirical formulation, as XTB (
https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/QS.html#METHOD),
and rerun with the level of theory that you want just the low energy ones.

Regards - Lucas Lodeiro


El mié, 13 ene 2021 a las 0:07, Fangyong Yan (<fyya... at gmail.com>)
escribió:

> Hi, Monu,
>
> To explore the free energy surface better, you may need to start at a high
> temperature, and then annealing down to the room temperature. And for each
> temperature, you can plot the radial distribution function, for your guest
> molecule and your MOF atoms, for example, at 800 K, 700 K, ...., 300K. The
> reason starting at high temperature is that you can use heat to get your
> guest molecule out of the potentially trapped free energy minima, so you
> can explore the free energy minima more completely.
>
> Regards,
>
> Fangyong
>
> On Tue, Jan 12, 2021 at 10:01 PM Fangyong Yan <fyya... at gmail.com> wrote:
>
>> Hi, Monu,
>>
>> You can run a molecular dynamics simulation at room temperature, for
>> several picosecond, and then you can plot the radial distribution function,
>> between your guest molecule and the MOF, by doing this you would have a
>> general picture of the free energy surface of your guest molecule in the
>> MOF. Then based on the free energy minima structures, you can start to
>> optimize your guest-MOF complex structure. (the free energy surface may be
>> different from the potential energy surface, but at least by doing MD
>> simulation and calculating the free energy surface based on radial
>> distribution function, you can have a basic idea about the free energy
>> surface, which should not be quite different from potential energy surface).
>>
>> Regards,
>>
>> Fangyong
>>
>> On Tue, Jan 12, 2021 at 7:20 PM Monu Joy <monuj... at gmail.com> wrote:
>>
>>> Hi there
>>>
>>> I have a general question: I would like to find out the global minimum
>>> of a guest molecule within the pore of a MOF. I know I can place the guest
>>> molecule in the pore and get the host-guest structure optimized, but if I
>>> would place the guest molecule in another position of the same pore, there
>>> also I can get the structure optimized. In this scenario how could I find
>>> the exact most probable location of the guest molecule within the MOF pore
>>> or its global minimum...?
>>>
>>> Any help would be highly appreciated...
>>>
>>> -Monu
>>>
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