[gmx-users] bilayers move apart by nanometers upon implementing dihedral restraints on lipid tails

[himanshu khandelia]

I am trying to implement dihedral restraints for lipids in a bilayer
using what is suggested here:

http://www.gromacs.org/Documentation/How-tos/Dihedral_Restraints

However, although the dihedral angles seem to be restrained fine, the
leaflets move apart by 10s of nanometers along +z over a nanosecond or
so, after which of course, the simulation crashes.

Can anyone suggest what I might be doing wrong?

 version 4.5.4

In the mdp file:

;dihedral restraints
dihre               =  yes
dihre_fc           =  100

In the topology:

[ dihedral_restraints ]

17 18 19 20 1    1    100    0    1    2
18 19 20 21 1    1    100    0    1    2
19 20 21 22 1    1    100    0    1    2
20 21 22 23 1    1    100    0    1    2
21 22 23 24 1    1    100    0    1    2
...
etc.

Himanshu