QM/MM with difficult embedding

[Phillip Seeber]

Dear CP2K community,
i am currently trying to setup a meaningful QM/MM setup for a doped sodium 
silicate glass. I would like to have some heavy metal atom and some of its 
surrounding silicates and sodium atoms in the QM part, while the rest of 
the glass shall be in the MM part. I have used a dissociative force field 
with Buckingham potentials for the sodium silicate glass, to allow proper 
melting of the glass during initial MD runs and would like to keep this 
force field. However, this force field relies on the partial charges of the 
Si, O and Na (2.4, -1.2, 0.6). The partial charges for the QM part, which 
interact with the MM part, additionaly to the Buckingham potentials, are of 
course not the same as those required by the force field. The result is, 
that the repulsive part of the Buckingham potential takes over and pushes 
all QM atoms away.
I would like to do assign "dummy charges" to the QM atoms (or its current 
positions) that are the charges of the corresponding MM atoms, while 
ignoring the charge distribution from the QM calculation. Otherwise the MM 
part should polarise the QM part as normal. Is there a way to achieve this?


Best regards
Phillip
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