[CP2K-user] Adjusting partial charges

Daniel Burns dbu... at iastate.edu
Thu Nov 12 21:08:02 UTC 2020


I'm looking at the tutorial @ https://www.cp2k.org/howto:biochem_qmmm.

The author recommends taking the charge from a side chain in the qm region 
and distributing it across the backbone atoms. "Do the same calculation for 
the 5 remaining mainchain atoms and check that the modified charges for the 
six atoms add up to zero".

1. Should these modified charges add up to zero or should they equal the 
negative of the charge in the qm region?

2. If my QM region has an overall charge with contributions from a ligand 
and ion, should the total charge of the qm region be distributed across 
backbone atoms and not just the charges from the side chains?  

3. Or instead to people counterbalance the qm region's charge by creating a 
net charge on the mm system with ions such that when the qm region is 
incorporated, the mm system becomes neutralized?  

4. I suppose if the latter route is taken, you must still neutralize 
partial charges from side chains in the qm region by distributing a counter 
charge on backbone atoms?

Thank you,

Dan Burns
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