[gmx-users] Problem about OPLS Fourier dihedraltypes vs Ryckaert-Bellemans

Erik Lindahl lindahl at stanford.edu
Wed Dec 25 15:25:59 CET 2002


I'm in Europe right now, but all the files in question are on my other
portable computer, so I can't check it in detail until I get back to 
the US
in January.

In general, though:

The aliphatic carbon parameters were updated during 1999/2000 by Bill 
and some additional parameters have been updated later by Kaminiski & 
These are included in the Gromacs version, but if your opls-aa file is 
older that might
explain the discrepancy.

I also recall that there was a factor two difference in the definition 
somewhere, but
I can't remember whether that was Amber/OPLS or if it was the improper 



On Wednesday, December 25, 2002, at 06:16  AM, pqchen at eyou.com wrote:

> Dear gmx-users:
>   In the official opls-aa force filed,the torsion parameters of the
> is V1=1.740kcal/mol,V2=-0.157kcal/mol,V3=0.279kcal/mol.(V0=?kcal/mol)
>   And in the gromacs Rychaert-Bellemans,the torsion parameters of the
> CT-CT-CT-CT is
> C0=2.93076KJ/mol,C1=-1.46538KJ/mol,C2=0.20934KJ/mol,C3=-1.67472KJ/mol,
> C4=0KJ/mol,C5=0KJ/mol;
>   Form the formula in the Gromacs manual,I find the formula as follow:
>   C0=V0+V2+0.5(V1+V3)
>   C1=0.5(3*V3-V1)
>   C2=-V2
>   C3=-2V3
>   C4=0
>   C5=0
> but I can't correctly translated OPLS Fourier dihedraltypes to Gromacs
> Ryckaert-Bellemans parameters.
>   Can anybody tell me how to correctly translated the Gromacs RB 
> parameters to
> the Official force field.(C#->V#)?
> --http://www.eyou.com
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