The auxiliary variables are coupled to a high temperature bath at T K, and the physical variables were coupled to another thermostat at T =300 K. We took T =1000 K for boosting the sampling of auxiliary variable space. We place M umbrella potentials centered at different values of s 1 coordinate, s 0 1,h . The harmonic coupling constant k α connecting CVs and auxiliary variables was taken as 4.48 × 10 3 kcal mol -1 Å 2 and mass µ α =150 amu for all the