how to calculate free energy - help

Hi, everyone!

I want to calculate the free energy of a nanoparticle in oil-water interface, displacing it in small distance from the interface and verifying the average of the forces acting on the nanoparticle.

Somebody have a sample input to perform this calculation or something?

Please help.

Thanks and regards,

Do you wish to obtain average forces or free energies? What kind of model are you interested in? Is the model/parameter set capable of describing an oil-water interface and the nanoparticle in one box?

In any case, it is usually suggested on this forum that you first demonstrate your work and effort by putting together an input deck by yourself, try it out, and come back with specific questions.

Cheers,
Ray

Hi, everyone!

I want to calculate the free energy of a nanoparticle in oil-water
interface, displacing it in small distance from the interface and verifying
the average of the forces acting on the nanoparticle.

please note that there is not just *the* free energy, but all kinds of
free energies and what you can usually measure are free energy
*differences*.

furthermore, there are multiple methods to compute free energy
differences/barriers and LAMMPS supports quite a few of them with
various facilities. for example, you can do thermodynamic integration,
metadynamics, adaptive biasing fore, steered MD, umbrella sampling.
and for several of them, there are multiple options.

Somebody have a sample input to perform this calculation or something?

from what you describe, it looks like you want to do umbrella
sampling. to get a solvation free energy difference.
this can be done via using fix spring or using the user-colvars fix.
it may also be worth considering using steered MD (and average over
multiple SMD runs).

in any case, more important than the "mechanics" of doing the
simulations is that you have a good understanding of the statistical
mechanical foundation of the process that you want to investigate and
how you extract the information you need. how you need to set up the
actual calculations will be straightforward after that.

axel.