[gmx-users] constant term in dihedral potential function
Kukol, Andreas
a.kukol at herts.ac.uk
Tue May 26 10:29:36 CEST 2009
Dear all,
I included the following dihedral potential function in a topology:
V(phi2) = -5.865 + 7.470 [1+cos(phi2-180°)] + 3.99 [1+cos(2 phi2)] + 1.1 [1+cos(3 phi2-180°)]
The problem is about representing the constant term -5.865. Using equation 4.61 (Gromacs 4.0 manual):
V(phi) = k * (1 + cos (n phi - phis) )
I specified:
V = -5.865 * (1 + cos (0 - 90) ) = -5.865 with multiplicity n=0
That leads to the entry in the topology file:
22 23 24 25 1 90 -5.685 0
This worked fine in Gromacs 3.3, but in Gromacs 4.05 I get the error message (from Grompp):
Fatal error:
Value of 'multiplicity' in Proper Dih. is 0, which is smaller than the minimum of 1
I wonder, if this is a bug in Gromacs 4.05, or if there is any better way to specify a constant term in a dihedral potential function.
Many thanks
Andreas
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