How to estimate QMMM box dimensions

[Rahul Hardikar]

Hello Matt,

Thanks for the prompt answer! Can you direct me to any publication where 
they have done such tests?

Regards,
Rahul

On Thursday, January 4, 2018 at 7:19:02 PM UTC+5:30, Matt W wrote:
>
> Probably it has just been done by checking that the results don't change 
> 'too much' in many cases.
>
> You could run an isolated molecule/cluster and use the MULTIPOLE 
> <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/POISSON/MULTIPOLE.html> 
> poisson solver (which is what you get when you use QMMM) and see how that 
> compares to say the WAVELET 
> <https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/POISSON/WAVELET.html> 
> one, and what cell dimensions are needed.
>
> Happy new year, too.
>
> Matt
>
> On Thursday, January 4, 2018 at 6:50:20 AM UTC, Rahul Hardikar wrote:
>>
>> Thanks for the reply Jiang,
>>
>> Maybe I should rephrase my question. I understand that GEEP algorithm 
>> implementation takes care of the QMMM electrostatic coupling, however that 
>> does not give an
>> idea of the box size for QM/MM region. What I am specifically referring 
>> to is the following section in QMMM:
>>
>> CP2K_INPUT <https://manual.cp2k.org/cp2k-2_6-branch/CP2K_INPUT.html> / 
>> FORCE_EVAL 
>> <https://manual.cp2k.org/cp2k-2_6-branch/CP2K_INPUT/FORCE_EVAL.html> / 
>> QMMM 
>> <https://manual.cp2k.org/cp2k-2_6-branch/CP2K_INPUT/FORCE_EVAL/QMMM.html> 
>> / CELL 
>> <https://manual.cp2k.org/cp2k-2_6-branch/CP2K_INPUT/FORCE_EVAL/QMMM/CELL.html>
>>
>> where the box size of the QM/MM region can be specified with possibly 
>> smaller dimensions than the entire cell. So do you or other users know a 
>> method to estimate the minimum 
>> dimensions of the QM/MM cell by looking at convergence with respect to 
>> some observable quantity in QMMM. Any help in this direction will be 
>> helpful!
>>
>> Best Regrads and belated New Year wishes to cp2k users!
>>
>> Rahul
>>
>>  
>> On Thursday, December 21, 2017 at 4:43:20 PM UTC+5:30, Tianshu Jiang in 
>> Beijing wrote:
>>>
>>> hello Hardikar,
>>>
>>> The dimension of QM box depends on your system, or the quantity where 
>>> you are interested. 
>>> You can refer the paper "An Efficient Real Space Multigrid QM/MM 
>>> Electrostatic Coupling" written by Teodoro Laino for details.
>>> The realization of QMMM in CP2K is based on this paper.
>>>
>>> Best wishes !
>>>
>>> 在 2017年12月20日星期三 UTC+8下午6:06:37，Rahul Hardikar写道：
>>>>
>>>> Dear CP2K Users/Experts,
>>>>
>>>> Currently, in my QMMM setup I am maintaining box lengths same as the 
>>>> overall systems' box lengths. I am aware that one can reduce the box size 
>>>> for the QMMM
>>>> box thereby reducing the cost of QM calculations. However what is not 
>>>> clear to me is the role of electrostatics when QMMM box lengths are less 
>>>> the the overall lengths. So my question is (a) how one can estimate the 
>>>> QMMM box lengths and maintain the electrostatic interaction between QM and 
>>>> MM part consistent? and (b) how can I estimate the amount of vacuum to use 
>>>> to avoid any interaction between periodic images? I am using cubecruncher 
>>>> to crunch out plane averaged electrostatic potential and hartree energy 
>>>> from the corresponding cube files.  
>>>>
>>>> Any suggestions and/or comments will be appreciated.
>>>>
>>>> Best Regards,
>>>> Rahul Hardikar
>>>>
>>>
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