GROMACS version: 2021.2

GROMACS modification: No

Hi all,

Hope someone can help me clarify this point:

I have the type 9 dihedral interaction in my forcefield files, and hope to further tune these values. The entries are:

; i j k l func phi0 kphi mult

CG321 CG321 NS1 CG321 9 0.00 6.9 1 ;

CG321 CG321 NS1 CG321 9 0.00 1.2 2 ;

CG321 CG321 NS1 CG321 9 0.00 3.1 3 ;

The I j k l atoms are exactly the same and the multiplicity values are 1 and 2. The user

s manual says “Type 9 allows multiple potential functions to be applied automatically to a single dihedral in the `[ dihedral ]`

section when multiple parameters are defined for the same atomtypes in the `[ dihedraltypes ]`

section.”

I do not quite understand this statement. I have one line in the [dihedrals] section of my .top file, which exactly hits the “CG321 CG321 NS1 CG321” dihedral.

Does it mean that the actual ff is the sum of the terms of

V = Kphi(1+cos(n*phi-phi0))

i.e. V_dih = 6.9*(1+cos(1 * phi - 0.0)) + 1.2*(1+cos(2 *phi -0.0 ) +3.1*(1+cos(3 *phi -0.0 ), ???

Hope someone can help me confirm this.