Fully periodic QM/MM simulations

[Jadzia]

Thank you for your answer Matt. 

Since error messages can be very helpful if they are precise, I would like 
summarize my understanding so far related to the error message I have 
gotten:

QM-QM long range correction not possible with COULOMB coupling.


Firstly, from what you wrote I implicitly conclude that the periodic 
section which I have added to my input file went into the direction of what 
you had in mind when you wrote about including the coupling of the QM 
region with the periodic MM images. In this case the above error message 
which I got seems to be not fully suitable since I had disabled the QM-QM 
long range correction (i.e. the MULTIPOLE section). To my understanding 
(which is admittedly incomplete) the problem might be of a more general 
nature and summarized as follows: *QM/MM long range correction not possible 
with COULOMB coupling*
because it seems to cover both cases QM-MM and optionally also QM-QM long 
term corrections (if the multipole section is not switched off) for the QM 
region. 

Secondly, the error message seems to be to general in another aspect, 
because you wrote that QM/MM periodic couplings are possible with DFT (and 
Coulomb coupling I guess), in which case the statement would only hold for 
certain QM methods. 






On Thursday, September 7, 2017 at 9:26:55 AM UTC+2, Matt W wrote:
>
> As I said, I wasn't sure if there was a periodic correction implemented 
> using Coulomb coupling for DFTB/semi-empirical.
>
> Looks like you just have to run without periodic coupling, or switch to 
> DFT to use periodic coupling.
>
> On Thursday, September 7, 2017 at 4:41:31 AM UTC+1, Jadzia wrote:
>>
>> Another thing I wonder about: Matt you said that I should keep the 
>> section QMMM periodic section so that the QM region feels the potential of 
>> the periodically replicated MM region. Which I would call a "MM-QM long 
>> range correction". But the error message of my last post states that 
>> a QM-QM long range correction is not possible with Coulomb coupling when I 
>> add this section. Therefore I wonder if the periodic section which I set up 
>> for the MM-QM long range correction was indeed what you had in mind...
>>
>
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