High dplumed values and zero exchange probability

[LubaSim]

Dear Plumed Users,

I'm running FEP/HREX simulation using Gromacs-2021.7 patched with plumed-2.8.3. However, I get zero probability exchange between the replicas and also high dplumed values, although the difference between the potential energy values in two adjacent replicas is not high. I would like to calculate manually the dplumed energy in order to check that.
According to the code /data/plumed-2.8.3/patches/gromacs-2021.7.diff/src/gromacs/mdrun/replicaexchange.cpp, dplumed is calculated as:
dplumed=adb * re->beta[a]+bdb * re->beta[b]

Could you please help me to understand how the values "adb" and "bdb" are calculated or where I can find them (I guess these are potential energies).

Thanks in advance,
Luba

[wu222222]

Replica exchange at step 99800 time 199.60001
Repl 1 <-> 2 dE_term = -0.000e+00 (kT)
dpV = 0.000e+00 d = 0.000e+00
Repl 1: adb = 1.532e+03 beta[a] = 3.880e-01; Repl 2: bdb = -1.082e+03 beta[b] = 3.880e-01
dplumed = 1.743e+02 dE_Term = 1.743e+02 (kT)
Repl ex 0 1 2 3 4 5 x 6 7 8 9 10 11
Repl pr .00 .00 1.0 .03 .21
me too.