# set up two variables for Phi and Psi dihedral angles 
phi: TORSION ATOMS=5,7,9,15
psi: TORSION ATOMS=7,9,15,17
#
# Impose an umbrella potential on CV 1 and CV 2
# with a spring constant of 500 kjoule/mol
# at fixed points on the Ramachandran plot
#
restraint-phi: RESTRAINT ARG=phi KAPPA=100 AT=LAMBDA1
restraint-psi: RESTRAINT ARG=psi KAPPA=100 AT=LAMBDA2

# monitor the two variables and the bias potential from the two restraints
PRINT STRIDE=10 ARG=phi,psi,restraint-phi.bias,restraint-psi.bias FILE=COLVAR UPDATE_FROM=50