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

[Sandeep Somani]

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 ? 

Thanks and Regards
Sandeep 

---
Research Associate
Computational Biology Group
Bioinformatics Institute
Singapore

http://web.bii.a-star.edu.sg/~ssomani/