[gmx-users] Discrepancy between Free Energy Perturbation using Gromos96 and OPLS

[Maik Goette]

Hi David

Could you be a bit more precise?
Is this difference due to a problem of united atoms/reaction field or 
all atoms/reaction field. For I also use FEP with all atoms 
(amber99-port) and reaction field, I could use some info. :)

Regards

Maik Goette, Dipl. Biol.
Max Planck Institute for Biophysical Chemistry
Theoretical & computational biophysics department
Am Fassberg 11
37077 Goettingen
Germany
Tel.  : ++49 551 201 2310
Fax   : ++49 551 201 2302
Email : mgoette[at]mpi-bpc.mpg.de
         mgoette2[at]gwdg.de
WWW   : http://www.mpibpc.gwdg.de/groups/grubmueller/


David wrote:
> On Sat, 2005-10-01 at 13:11 +0800, Sandeep Somani wrote:
> 
>>hi all 
>>
>>I did a Slow Growth (dummy -> real) based FEP of a small ligand bound to
>>a protein using Gromos and OPLS ff. 
>>Description of ligand in both cases is identical. 
>>
>>Free energy change from the Gromos simulation is reasonable but the
>>number from OPLS is an order of magnitude more negative. 
>>
>>All parameters (reaction field electrostatics, constraints in topology,
>>delta-lambda etc) other than the ff are identical. Am using gmx3.2.1.
>>
>>Has anyone encountered this before ? what could be the origin of this
>>discrepancy ? 
> 
> It could be due to the all-atom/united atom difference in combination
> with the reaction field. Berk has recently implemented an exclusion
> correction for reaction fields that could be important here. You could
> retry it with 3.3beta to see whether there is a difference.
> 
> 
> 
>>Thanks and Regards
>>Sandeep 
>>
>>---
>>Research Associate
>>Computational Biology Group
>>Bioinformatics Institute
>>Singapore
>>
>>http://web.bii.a-star.edu.sg/~ssomani/
>>
>>
>>
>>
>>
>>
>>
>>
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