Hi, The numerical derivative for the Nth value y[N] is calculated as: der = y[N+1] - y[N-1] * 0.5 * deltaX where y is the potential deltaX is the difference between two successive values in your input (e.g., 1 if you have a table that goes from -180 to 180 with 361 values).
I don't think you can print the number without changing the code, but it's not difficult to calculate. You can plot your forces and -der and see where they deviate. Ran. hong bingbing wrote: > Hi, Ran, > > The potential f(x) and force -f'(x) in the table are calculated by > myself before constructing the table. The potential can be written in > an analytical form and the force is calculated as the analytical > negative derivative of the potential at point x. There should not be > so large deviation betw. the value I supplied and the value calculated > by GROMACS. Wait. Is there something wrong in my interpretation? > What's your method to get the force? Is there a way to see the > numerical derivative generated by GROMACS? > > Thanks > CH
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