Non-integer charge in the classical part of QM/MM system

tarak karmakar tarak... at gmail.com
Fri Jul 31 18:34:26 CEST 2015


Dear All,
I am trying to study an enzymatic reaction of an enzyme using CP2K. While
running the QM/MM simulation I notice the following,

 CHARGE_INFO| Total Charge of the Classical System:
1.170000
 DFT|
Charge                                                                  -2

>From an old post
https://groups.google.com/forum/#!searchin/cp2k/charge$20QM$2FMM/cp2k/1BGZ2N3fSKc/J9E5HjI1o4cJ
 I realize that the user should take care of the non-integer charge, if it
is there.

In my system, the reaction substrates in the active site have a total -2
charge while the surrounding amino acids are all neutral. Thus in the DFT
section I have mentioned the following,
&DFT
     CHARGE -2
     BASIS_SET_FILE_NAME  ./GTH_BASIS_SETS
     POTENTIAL_FILE_NAME  ./GTH_POTENTIALS

I have checked my .psf file, and the sum of all the atomic charges of the
system is zero.

So, my query is whether the partial charge arises due to the inappropriate
selection of amino acid fragments in the QM region?
I would appreciate if someone could help me in this issue.

Thanks,
Tarak
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