[gmx-users] QMMM free energy

[Robert fiske]

>Maybe I misunderstand you, but quantum programs are not likely to work with 
>fractional charges. If you do the charge change in the MM part it may be 
>possible (but it is definitely not implemented)

I did some tests with CPMD and it appeared to work with fractional charges, 
I took a simple water molecule and ran a series of calculations changing the 
charge input from -1 to +1 by increments of .2, I then had someone look at 
the esp values CPMD gave me for each run and he felt that the results looked 
correct.  However, I'll send an email to the CPMD list to see if this was 
just coincidence or if it is indeed implemented in their code.  From what I 
remember the CPMD code does use a floating point variable to hold the charge 
data, although they may have other reasons for doing so.

fiske

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