[gmx-users] QMMM free energy

[David van der Spoel]

Robert fiske wrote:
> 
>> I'm not a QM expert myself (Gerrit, comments?),  but I'm pretty sure  
>> the main reason is that you cannot either mutate atom types or  
>> decouple interactions gradually in the QM part of the system. Once  
>> this is solved for a pure QM system it should be straightforward to  
>> implement the QM/MM interface of it.
> 
> One of the main things we plan to do with the free energy code (once I 
> can confirm I'm doing things right) is to modify the charge of the 
> quantum system for the lambda values, so atom types don't need to be 
> modified for this I believe, although I see how that could complicate 
> other types of free energy calculations.  As for decoupling interactions 
> I don't know what impact that has for changing of charge.
> 
> For now, are there any major complications if all we want to do is 
> modify the charge from state A to state B (assuming the interaction 
> problems you mentioned aren't a problem)
> 
> 
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)

-- 
David.
________________________________________________________________________
David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se
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