Metadynamics using plumed + ipi

[Sriram Vignesh AK]

Hello everyone,

I am trying to estimate quantum free energy barrier for an isomerization process using i-pi and plumed. The barrier height for the reaction is around 25 kcal/mol(~105 kJ/mol). So i am using the following plumed input.
# default units are LENGTH=nm ENERGY=kJ/mol TIME=ps
#MOLINFO STRUCTURE=rctnt_E.xyz
q: TORSION ATOMS=4,9,7,8 #H5-N3-C1-N2
mtd: METAD ARG=q PACE=20 SIGMA=0.35 HEIGHT=80.00 FILE=plumed/HILLS BIASFACTOR=100 TEMP=300 GRID_MIN=-pi GRID_MAX=pi

PRINT ARG=q  STRIDE=1 FILE=plumed/COLVAR
FLUSH STRIDE=1

I am applying a bias on the required dihederal(RC).The system is diffusing between the two barriers as expected - but when i plot the free energy profile one of the wells is deeper than other depending on which well the system is in at the time of plotting the profile(whereas both are isoenergetic).
so there is no convergence instead the profile keeps shifting between making one of these two minima deeper.

Is there something wrong with the way I am doing the things? I am plotting fes like this
plumed sum_hills --min -pi --max pi --bin 101 --stride 100 --mintozero --hills plumed/HILLS > fes.dat

Thanks for the help

Regards,

Sriram