Custom Potential

[Santiago Movilla]

Hello PLUMED community,

I want to set the bias potential of an angle so that the system mostly stays in the "allowed" states. Basically, I have an angle that I want to keep between 70-90 deg or between 140-170 deg. I've thought I could achieve this by adding lower and upper walls at the limits and a Gaussian repulsion potential (a bit shifted to account for the asymmetry of the ranges). However, I'm not sure if my implementation is correct or even if it is the simplest and cleanest way to do it.

Could someone please advise or guide me on this problem?, I would be very grateful.

Idea:

theta: ANGLE ATOMS=1,2,3

# Walls in 70° (1.22173) y 170° (2.96706)
lwall: LOWER_WALLS ARG=theta AT=1.22173 KAPPA=1000.0 EXP=2 EPS=1 OFFSET=0
uwall: UPPER_WALLS ARG=theta AT=2.96706 KAPPA=1000.0 EXP=2 EPS=1 OFFSET=0

# Repulsive Gaussian in 120° (2.0071 rad)
repulsion: CUSTOM ARG=theta FUNC="5.0*exp(-((theta-2.0071)^2)/(2*0.04))" PERIODIC=NO

# Apply bias?
BIASVALUE ARG=repulsion

Santiago Movilla