interaction energy between a nanoparticle and h2o molecule

Dear all,
To find out the interaction energy (vdwl) in LAMMPS, I created a spherical nanoparticle and a water molecule. What I found out that this energy decreases with increase in distance of water molecule from the nanoparticle which is obvious. But when I am increasing the nanoparticle size the energy varies. I am doing this so that I can compare this Molecular mechanics energy with the obtained energy from quantum mechanics. I did this to avoid using the mixing rule for nanoparticle and water interaction.

Also, is it okay to use any mixing rule even though nanoparticle ( vashsihta potential)uses one potential and water (lj potential)uses some other potential?

Thank You!

Dear all,
To find out the interaction energy (vdwl) in LAMMPS, I created a spherical
nanoparticle and a water molecule. What I found out that this energy
decreases with increase in distance of water molecule from the nanoparticle
which is obvious. But when I am increasing the nanoparticle size the energy
varies. I am doing this so that I can compare this Molecular mechanics
energy with the obtained energy from quantum mechanics. I did this to avoid
using the mixing rule for nanoparticle and water interaction.

you are not making *any* sense here.

Also, is it okay to use any mixing rule even though nanoparticle (
vashsihta potential)uses one potential and water (lj potential)uses some
other potential?

what kind of formula would you apply? how can you mix epsilon and
sigma of a lennard jones potential with a potential that doesn't use
those?

axel.

Dear Sir,
Thank you for the reply.
The question I asked meant that to define the pair coefficient between a nanoparticle and atoms of water, LB mixing rule was used in most of the papers i.e we have a copper nanoparticle with lj parameters and water with lj parameters. But to cross check that I have done quantum mechaincs energy calculation which should match the energy obtained from LAMMPS if the mixing rule approximation is correct. Thank you!

Dear Sir,
Thank you for the reply.
The question I asked meant that to define the pair coefficient between a
nanoparticle and atoms of water, LB mixing rule was used in most of the
papers i.e we have a copper nanoparticle with lj parameters and water with
lj parameters. But to cross check that I have done quantum mechaincs energy
calculation which should match the energy obtained from LAMMPS if the mixing
rule approximation is correct. Thank you!

this is not a LAMMPS question, but a question about validity and
comparability of different methods. this is off-topic for this list
and besides, there is no way to answer this question at this general
level.

axel.