Hello,

In summary, I’m using pair_styel buck/coul long long with ewald/n and even though I define pair_coeff for each atom type interaction my log file says:

WARNING: Geometric mixing assumed for 1/r^6 coefficients

I’m using lammps with the user-ewaldn package. I’m using ewald to calculate the dispersion and coulombic long range interactions using this command. I have an interface and some voids and sometimes non orthogonal lattice vectors so ewaldn is my best choice and I think using it to also calculate the van derwaals dispersion is better suited to these interfaces than a correction force. I am using atom_style full and have 5 types of atoms in my simulation and define the partial charges along with the xyz coordinates and bond connectivity in a data file. This is my input file for the potential where I explicitly define my pair potential for each atom type:

bond_style harmonic

angle_style harmonic

dihedral_style harmonic

improper_style harmonic

pair_style buck/coul/long 10.0 10.0

kspace_style ewald/n 1.0e-4

pair_coeff 1 1 14976.00 0.323625 640.80

pair_coeff 1 2 30183.57 0.291121 566.03

pair_coeff 1 3 30183.57 0.291121 566.03

pair_coeff 1 4 33702.40 0.279642 505.60

pair_coeff 1 5 4320.000 0.292826 138.20

pair_coeff 2 2 60833.90 0.264550 500.00

pair_coeff 2 3 60833.90 0.264550 500.00

pair_coeff 2 4 67925.95 0.255037 446.60

pair_coeff 2 5 12695.88 0.265957 116.96

pair_coeff 3 3 60833.90 0.264550 500.00

pair_coeff 3 4 67925.95 0.255037 446.60

pair_coeff 3 5 12695.88 0.265957 116.96

pair_coeff 4 4 75844.80 0.246124 398.90

pair_coeff 4 5 14175.97 0.256345 104.46

pair_coeff 5 5 2649.700 0.267380 27.400

In my log file I get the following:

pair_style buck/coul long long 10.0 10.0

WARNING: Geometric mixing assumed for 1/r^6 coefficients

WARNING: Using largest cut-off for buck/coul long long

kspace_style ewald/n 1.0e-4

in the manual it says:

“This pair styles does not support mixing. Thus, coefficients for all I,J pairs must be specified explicitly.”

So I’m not sure why it is doing geometric mixing. I created a restart file and then converted the restart file using the restart2data tool and it shows geometric mixing. I also compared a bunch of single point energies (run 0) between lammps and another program and they were almost identical but these were for a deforming a single molecule with no long range contributions (ewald) bu they did have short range vdw and coulombic forces which did not show mixing.

Any help would be great. Thanks Lynn