pair_coeff definition involving hybrid pair style mm3 and lj

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1

Dear lammps users,

I am testing a MOF system with small molecules, and the force field is mm3 and TraPPE respectively, so I use a hybrid pair_style, but I don’t know how to mix them. I know “pair_modify mix geometric” is not supported here, but to define pairs coeff like 1-10 involving two pair styles is confusing to me. But I have to define them otherwise there is the error “All pair coeffs are not set”.

Thank you for any suggestion!

Luyi

#for MOF with small molecules system
pair_style hybrid mm3/switch3/coulgauss/long 12.0 3.0 lj/cut/coul/long 12.000

pair_coeff 1 1 mm3/switch3/coulgauss/long 0.059 1.82 1.2

pair_coeff 2 2 mm3/switch3/coulgauss/long 0.059 1.82 1.2

pair_coeff 3 3 mm3/switch3/coulgauss/long 0.367 3.52 1.2

pair_coeff 4 4 mm3/switch3/coulgauss/long 0.02 1.6 1.2

pair_coeff 5 5 mm3/switch3/coulgauss/long 0.059 1.82 1.2

pair_coeff 6 6 mm3/switch3/coulgauss/long 0.056 1.96 1.2

pair_coeff 7 7 mm3/switch3/coulgauss/long 0.056 1.96 1.2

pair_coeff 8 8 mm3/switch3/coulgauss/long 0.056 1.94 1.2

pair_coeff 9 9 mm3/switch3/coulgauss/long 0.02 1.62 1.2

pair_coeff 10 10 lj/cut/coul/long 0.0199 4.3

pair_coeff 11 11 lj/cut/coul/long 0.1946 3.75

pair_coeff 12 12 lj/cut/coul/long 0.0000 0.000

pair_coeff 13 13 lj/cut/coul/long 0.1846 3.02

When I was testing the MOF system only, I used “pair_modify mix geometric”, and it worked well.

2

Dear lammps users,

I am testing a MOF system with small molecules, and the force field is mm3 and TraPPE respectively, so I use a hybrid pair_style, but I don’t know how to mix them. I know “pair_modify mix geometric” is not supported here, but to define pairs coeff like 1-10 involving two pair styles is confusing to me. But I have to define them otherwise there is the error “All pair coeffs are not set”.

this is just one of the pitfalls of mix and matching completely different force fields. most of the time this is just giving you bad results, sometimes people get lucky, and then you just have the situation, where there is no simple way out.

since - as you already noted - there is no automated way to generate the parameters for the mixed interactions, you have to specify them explicitly. which means, that you have to parameterize those interactions, preferably, so that all interactions use the same pair style.

axel.