read_data with Pair Coeffs

Hello,

I have written a data file with many particle species since I want to generate polydisperse ensemble of particles interacting via the Morse potential.

Ane example of it is the following:

LAMMPS Description

4 atoms

4 atom types

0 47.13 xlo xhi
0 47.13 ylo yhi
0 47.13 zlo zhi

Masses

1 0.500363
2 0.519426
3 0.477395
4 0.511256

Pair Coeffs # morse

1 8.1 33 0.984983
2 8.1 33 0.997337
3 8.1 33 0.969675
4 8.1 33 0.992079

Atoms

1 1 46.4506 15.1946 24.5231
2 2 9.79043 6.54441 14.5177
3 3 33.7927 31.4994 34.9494
4 4 27.3936 7.11498 38.2475

My input script reads the following:

units lj
atom_style atomic
boundary p p p

pair_style morse 1.4
pair_modify shift yes mix arithmetic

read_data begin.lmp

velocity all create 1 87287 loop geom

fix 1 all nvt temp 1. 1. 5.

thermo 1000

timestep 0.01

dump MYDUMP all atom 1000 dump.lammpstrj
dump_modify MYDUMP sort id
run 1000

The issue is that when I get the error "All pair coeffs are not set (…/pair_morse.cpp:214)” when I try to run the script.

No error occurs if instead I provide a file with the PairIJ Coeffs section instead of Pair Coeff. The issue is therefore with the mixing rules.

Oddly enough, if I use write_data with "pair ii” on, the resulting file cannot be read in input by my script, and the error occurs again. I therefore imagine that I am doing something wrong in the implementation of the mixing rules, but the documentation explicitly indicates that when using Pair Coeffs the mixed coefficient "will be generated automatically by the pair style’s mixing rule”.

Thank you in advance

Hello,

I have written a data file with many particle species since I want to
generate polydisperse ensemble of particles interacting via the Morse
potential.

Ane example of it is the following:

​[...]

The issue is that when I get the error "All pair coeffs are not set
(../pair_morse.cpp:214)” when I try to run the script.

​as you should. the morse pair style does not support mixing. please see
the corresponding section​
LAMMPS Molecular Dynamics Simulator

No error occurs if instead I provide a file with the PairIJ Coeffs section
instead of Pair Coeff. The issue is therefore with the mixing rules.

Oddly enough, if I use write_data with "pair ii” on, the resulting file
cannot be read in input by my script, and the error occurs again

​you *have* to use the "pair ij" ​ option. with "pair ii" LAMMPS will only
write out the parameters for the Pair Coeffs section, and as stated before
that is not support with the morse style.

. I therefore imagine that I am doing something wrong in the
implementation of the mixing rules, but the documentation explicitly
indicates that when using Pair Coeffs the mixed coefficient "will be
generated automatically by the pair style’s mixing rule”.

​*if* the pair style supports mixing, but this is not the case here.

axel.