reproduce the recipe

[Francesco]

Hi all,

I'm trying to reproduce, STEP by STEP the SN2 reaction of JPC-B 2005,
109 6676-6687, "A
recipe for the computation of the free energy barrier and the lowest
free energy path of
concerted reactions".

I am trying to setup the 2nd and 3rd terms on the right of Eq. 4. No
problems to setup
the mass of the fictious particle (2nd term). How should I write the
force constant k_a
and the reference position for the 3rd term ?
Is the quadratic wall (K,POSITION) the right solution ?

thanks,
Francesco