From NWChem
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8:15:14 AM PST  Wed, Nov 23rd 2011 

Hi,
I am using the QM/MM method in NWChem to do some geometry optimization. I have noticed that, in principle, the QM region can be constrained to a certain point group since in NWChem the MM charges are not electrostatically embedded in the QM calculation. However, I cannot find a way to carry out such kind of calculation. I just wonder whether there is way to do that or should I edit the source code to enable such a feature?
Peizhi




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1:17:43 PM PST  Tue, Nov 29th 2011 

It would not be possible to do it in the current version. I also do not understand why it would be useful, since the MM environment would in general destroy any symmetry





1:31:24 AM PST  Wed, Dec 7th 2011 

Dear Marat,
Thanks for your reply.
I am just experimenting with methods of optimizing geometry of the solute molecule in solution. It would be nice if the symmetry could be constrained during the QM/MM optimization since this would help to reduce computational costs in the subsequent highlevel calculations on the solute molecule. The physical thought is, if we observed the solution dynamically over a period of time, though the symmetry of the solute would be destroyed by the MM solvents at each instant, certain symmetry would still be preserved from a statistical point of view.
According to my understanding of the QM/MM implementation in NWChem, such kind of symmetryconstrained optimization would be feasible after some modification of the source code. I just wonder which part of the code I should get started with.
Peizhi




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9:38:13 AM PST  Wed, Dec 7th 2011 

I have to look in the code to see if there is an easy way to do it.
Marat



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