Free energy of insertion

Thanks Dr. Axel for your suggestion to use fep. I dont think I want to perturb the parameters of the potential. I would like to get the change in potential energy after insertion with less computational effort.
Is there any compute/fix that does this ?

Arun

Thanks Dr. Axel for your suggestion to use fep. I dont think I want to
perturb the parameters of the potential. I would like to get the change in
potential energy after insertion with less computational effort.

but how is this energy defined? if you stick your molecule into an
arbitrary location, you could just as well pick a random number. if
you want to find the location available with the lowest energy, you
need to make a *huge* number of insertion attempts (and then there is
the question if you want to relax the matrix or not. at that point you
could, for example, just as well run a grand canonical ensemble and
adjust the chemical potential until you get a specific desired
occupation.

Is there any compute/fix that does this ?

you are asking the wrong question. what you have to look for is a term
that better describes the process you want to investigate on the
microscopic level. the rest will follow automatically. without having
a lot of experience myself in this area, i have to say that either FEP
or perhaps TI seem quite attractive.

i guess at this point, you need to do a proper survey of the
literature and see what kind of methods can be applied, what quality
of answer it would give you, and whether that is sufficient for your
needs. it is very difficult to suggest to use any feature in LAMMPS,
if the description of the model is this vague and unspecific.

axel.

Sounds like you are trying to do what have been done here:
http://pubs.acs.org/doi/abs/10.1021/ct200787v

or here:
https://www.nersc.gov/assets/pubs_presos/kimjscidac.pdf

Hope the paper helps you,

Carlos