Various Hints

What bin size should I choose for ABF?

The ABF method calculates the mean force in each bin and applies this force back to the system to remove energy barriers and enable free diffusion throughout the sampling space. The optimal bin size depends on the shape of the free energy derivative - how much is the mean force changing along the coordinate. A good starting value might be 0.5 A, but if the derivatives curve is not smooth, you will have to go for smaller values. It is in your interest to keep the bin size as large as possible, because smaller bins take a longer time to converge.