From: ABEL Stephane (
Date: Thu Jan 26 2017 - 03:37:43 CST

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