Hybrid AIREBO and LJ for methane molecules

Dear all,

I have several CH4 molecules and want to have AIREBO interaction inside CH4 and LJ interaction between each molecules. How can I tell lammps to distinct between C-H interaction inside molecule ( covalent C-H) and between molecules (non-covalent C-H)?

I have used the following commands but it consider all C-H interactions as covallent bond (AIREBO).

pair_style hybrid AIREBO 3 1 1 lj/cut 10
pair_coeff * * AIREBO CH.AIREBO C H

pair_coeff 1 1 lj/cut 73e-5 2.81

pair_coeff 2 2 lj/cut 42e-4 3.35

How can I set pair_coeff 1 2 to consider AIREBO inside CH4 and LJ between C and H atoms in two different molecules?

Mohyeddin

Dear all,

I have several CH4 molecules and want to have AIREBO interaction inside CH4
and LJ interaction between each molecules. How can I tell lammps to
distinct between C-H interaction inside molecule ( covalent C-H) and between
molecules (non-covalent C-H)?

I have used the following commands but it consider all C-H interactions as
covallent bond (AIREBO).

pair_style hybrid AIREBO 3 1 1 lj/cut 10
pair_coeff * * AIREBO CH.AIREBO C H
pair_coeff 1 1 lj/cut 73e-5 2.81
pair_coeff 2 2 lj/cut 42e-4 3.35

How can I set pair_coeff 1 2 to consider AIREBO inside CH4 and LJ between
C and H atoms in two different molecules?

it is a pointless exercise anyway, since there is practically no
benefit to using AIREBO for the C-H interactions. most people that
simulate methane don't even simulate the hydrogens explicitly, but use
united atom model. apart from that, you'll probably get as good a
representation (if not better) from using something like OPLS/AA or
similar.

axel.

If you decide to stick with AIREBO, please note that AIREBO already includes LJ interactions between all atom pairs.

Ray

2014-12-01 15:42 GMT+01:00 Mohyeddin <[email protected]>:

Dear all,

I have several CH4 molecules and want to have AIREBO interaction inside
CH4 and LJ interaction between each molecules. How can I tell lammps to
distinct between C-H interaction inside molecule ( covalent C-H) and
between molecules (non-covalent C-H)?

Using AIREBO will do that automatically for you, in the sense that it
includes LJ-style nonbonded interactions anyway (between nonbonded atoms).
If you're not satisfied by that way it does that, using pair_stule hybrid
will not work because it does not allow to differentiate between
interactions the way you want it: such "complex" rules should only be
handled by actual code such as a real pair_style.

Kristof