Question on "neigh_modify binsize"

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1

Dear lammps members,

I have a small argon nvt simulation of 810 atoms at 125K and density 1349 kg/M^3. Domain size in angstroms: 54 X 27 X 27.

(The sigma for argon LJ potenial is 3.4 angs)

I am using:

units real

atom_style atomic

pair_style lj/cut 22.00

As I vary the cut-off size from 7 to 22, the simulation runs fine and reaches
equilibrium pressure at 125K.

When I increase cutoff size to 33, I get an error

“Neighbor list overflow, boost neigh_modify one …”

So I set “neigh_modify binsize 1.0” and the simulation runs.

I want to clarify what I actually did.
The documentation on neigh_modify says that

  1. default for bin size is 1/2 cutoff; and if bin size is set to 0, the default is still 1/2 cutoff for neighbor list computations.

  2. the bin size must be specified in distance units.

Is my usage of “neigh_modify” command correct:
setting binsize to be 1.0 is correct and that it is infact equal to setting the binsize to 33 angs for neighbor list computation.

regards
shankar

2

When I increase cutoff size to 33, I get an error
“Neighbor list overflow, boost neigh_modify one …”

This error message actually meant to increase “one”, not “binsize”.

So I set “neigh_modify binsize 1.0” and the simulation runs.

This is a very very small binsize. From the doc page “If you make it too small, the optimal number of atoms is checked, but bin overhead goes up.”

I want to clarify what I actually did.
The documentation on neigh_modify says that

  1. default for bin size is 1/2 cutoff; and if bin size is set to 0, the default is still 1/2 cutoff for neighbor list computations.

  2. the bin size must be specified in distance units.

Is my usage of “neigh_modify” command correct:
setting binsize to be 1.0 is correct and that it is infact equal to setting the binsize to 33 angs for neighbor list computation.

No, they are not the same at all.

R.

3

Dear Ray,

Thank you for the clarification.

I now see the keyword “one” for “neigh_modify”.

shankar