Is it possible to make angle restraints between two values?

User discussions
1

GROMACS version: 2018.4
GROMACS modification: No
I have a problem. I want to run a 100 ns simulation with flex angle C3-C6-C7 between 130-160 degrees in lutein. This is my angle
flex_angle
How to implement this in topology?
I found an implementation of dihedral
like

[ dihedral_restraints ]
; ai   aj    ak    al  type  phi  dphi  fc
58 59 61 63 0 10 0 1000

or position restraints
http://www.gromacs.org/Documentation_of_outdated_versions/How-tos/Position_Restraints

Here I can’t see Restraints — GROMACS 2021.3 documentation what I should write in my topology file (I see only theory in section angle restraints) to use these restraints in my simulation.

In addition, I see only Flat-bottomed position (not angle) restraints, so to implement restraints of flex angle between 130-160 should I use position restraints instead of angle restraints?

2

Hi,
one can apply angle restraint to restrain the angle between two pairs of particles or between one pair of particles and the z-axis (see eq. 9-10)
https://manual.gromacs.org/current/reference-manual/functions/restraints.html
(for the syntax see Table 14 File formats — GROMACS 2021.3 documentation).

As far as I understood, you want that the angle can vary between two values without penalty. In that case you can try to restraint the distance between C3 and C7 using a potential as the one Fig 31 ( Restraints — GROMACS 2021.3 documentation )

Kind regards
Alessandra

1 Like
3

Thank you so much. Distance restraints is a great idea and I checked and it works very well in my situation

4

; restraints for angles
[ intermolecular_interactions ]
[ angle_restraints ]
;i j k l type theta fc multiplicity
1608 1610 4651 4645 1 180.0 2000 1
is this correct format; i want to restrain 1610 4651 4645 at 180 degrees.