[gmx-users] OPLS and RB parameters in GROMACS

[Andrew Paluch]

There is no error. The alkane dihedral parameters were updated in 1999, and
differ from those originally published in 1996.

Andrew

On Tue, Feb 8, 2011 at 5:20 AM, sulatha M. S <mssulatha at gmail.com> wrote:

> 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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