Hi all, Hi
I've converted the OPLS-AA torsional potential parameters for the alkane C-C-C-C (CT-CT-CT-CT in the gromacs parameter file notation), C-C-C-H (CT-CT-CT-HC), and H-C-C-H (HC-CT-CT-HC) torsions from the OPLS format given in Jorgensen et al, JACS 118, 11225 (1996) to the Ryckaert-Bellemans format given in ffoplsaabon.itp and found that the calculated values are different. A previous post to the gmx-users mailing list on March 27, 2008, pointed out this issue for the H-C-C-H torsional potential but there was no response to that. Does anyone know if there is an error in the ffoplsaabon.itp file? Or is there a newer set of OPLS-AA parameters? For the OPLS-AA parameters (in kcal/mol), I used: dihedral V1 V2 V3 C-C-C-C 1.740 -0.157 0.279 C-C-C-H 0.0 0.0 0.366 H-C-C-H 0.0 0.0 0.318 from which I calculated the Ryckaert-Bellemans parameters (in kJ/mol) as: dihedral C0 C1 C2 C3 C-C-C-C 3.56686 -1.889076 0.65688 -2.33467 C-C-C-H 0.66526 1.99577 0.0 -2.661024 H-C-C-H 0.76567 -2.29702 0.0 -3.06269 the parameters in the ffoplsaabon.itp file are: dihedral C0 C1 C2 C3 C-C-C-C 2.9288 -1.4644 0.2092 -1.6736 C-C-C-H 0.6276 1.88280 0.0 -2.5104 H-C-C-H 0.6276 1.8828 0.0 -2.5104 Thankyou for any clarification. Sulatha
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