VMD-L Mailing List

From: Mayne, Christopher G (cmayne2_at_illinois.edu)
Date: Wed Feb 01 2017 - 14:29:33 CST

Stéphane,

There’s not really enough information here to make any specific claims about your parameters. I will note that dihedrals described by multiplicities > 1 tend to have one dominant term while additional terms refine the shape.

Did you try the fitting only using n=3, as suggested from the ParamChem output?

Regards,
Christopher Mayne

> On Jan 26, 2017, at 3:37 AM, ABEL Stephane <Stephane.ABEL_at_cea.fr> wrote:
>
> Dear vmd/fftk users,
>
> I am currently optimizing some torsions of the propyl diaminoxude molecule (CH3-(CH2)-NO(CH2)2 with fftk (vmd 1.9.3) but I am not sure if my approach is correct. For instance for the CCNO torsion* I obtain the following values** that fit well the QM curve (FINAL RMSE 0.174) obtained from GAUSSIAN
>
> Suggestion from ParamChem (CG321 CG324 NG3P0 OG312 0.2600 3 penality 58.0)
>
> **dihedral {CG321 CG324 NG3P0 OG312} 4.200 1 180.00
> dihedral {CG321 CG324 NG3P0 OG312} 0.591 2 180.00
> dihedral {CG321 CG324 NG3P0 OG312} 0.722 3 0.00
>
> As you can see that force constant for the first periodicity is quite higher than the other values and force constants for all the dihedral in the cgenn.ff parameter listing. Is it possible or I missing something?
>
> Thank you in advance for your comments
>
> Stéphane
>
>