[gmx-users] ffG43a1.rtp file error

[rob yang]

Hi Ken,

>#define gd_9      0.000       3.14          2

0.000 = phase shift. it takes on values of 0 or 180.
3.14 = force constant in KJ/mol
2 = multiplicity of the torsion term

the torsion equation is: Sum of {(Force constant)/2*(1+cos(phase 
shift)*cos(multiplicity * your angle))}
it can theoretically go up to 6 terms (multiplicities)

it seems like there are two terms in this particular torsion, so if you are 
sure that this is indeed your dihedral angle, you can add two lines to your 
.itp file:
2     1     4     5     1 gd_9
2     1     4     5     1 gd_11

hope that helps.

Rob