cp2k COMBINE_COLVAR/FUNCTION define exponential form function

[Sun Tao]

Dear All:

I am trying to set up some collective variables in cp2k. I need to 
calculate the exponential-form value of a defined collective variable, 
which is the distance between certain 2 atoms, the form is as the following:

f = 1/{1 + exp([distance(i, j) - 0.5]/1.5)}

Shall I define the CV as the following?

  &SUBSYS
    &COLVAR
       &COMBINE_COLVAR
          &COLVAR
             &DISTANCE
                ATOMS 1 5

             &END
          &END COLVAR
          FUNCTION 1/(1+exp((CV-0.5)/1.5))
          VARIABLES CV1 
          ERROR_LIMIT 1.0E-8
       &END
    &END

   &END



Or the correct form should be something else? Thanks ~


Tao





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