format your data for 2D-WHAM with 1D being the distance and the 2nd-D being your other coordinate of interest. Specify a value of zero for the force constants for your 2nd-D. Run 2D-WHAM. Boltzmann project the 2D PMF onto your 2nd-D.

I think you can also do essentially the same thing by re-weighting using the F-values from 1D-WHAM, but I find the above method to be the simplest. It also provides you with a 2D free energy profile, which can be informative both biologically and to indicate on sampling problems.

Note that you're very likely going to run into convergence problems since your 2nd-D will rely on brute-force to converge, and worse: the umbrellas in 1D can force the sampling in the 2nd-D to surmount energy barriers that might be circumvented in unrestrained sampling.

Chris.

-- original message --

Qian Wang wrote:
Hi,

I used umbrella sampling method to restrain the distance of two
molecules at several distances. Then I can use g_wham to get the free
energy as a function of the distance. Is there any way that I can get
the free energy as a function of another parameter? Thanks a lot.


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