Using hybrid/overlay to model (buck+coul) & (morse+coul) of PCRIM potential for SiO2

Dear LAMMPS users,

I am trying to model Silica crystal at 1000k. The short range interactions ofSi-Si,Si-O and O-O atoms are modeled with Morse potential. The long-range electrostatic interactions are modeled with comb potential.

I wrote the following commands to model these interactions, but the temperature of the system from the NVT simulations is unreasonably high at the first step (over 3000K).

units metal
atom_style charge
boundary p p p

read_data SiO2.data

mass 1 28.0855
mass 2 15.9994

pair_style hybrid/overlay morse 9.0 comb
pair_coeff 1 1 morse 0.007695 2.0446 3.7598
pair_coeff 1 2 morse 1.99597 2.6518 1.628
pair_coeff 2 2 morse 0.23272 1.3731 3.791
pair_coeff * * comb ffield.comb Si O

neighbor 0.3 bin
neigh_modify delay 5

compute pe1 all pe/atom
compute ke1 all ke/atom
compute F_temp all temp

thermo 100
thermo_modify temp F_temp lost ignore norm yes

timestep 0.001

velocity all create 1000 213789
fix 1 all nvt temp 1000 1000 0.05 #iso 0.0 0.0 0.5 drag 0.2
fix 2 all qeq/comb 10 0.001

dump 1 all custom 1000 SiO2-melt.lammpstrj id type x y z c_ke1 c_pe1
restart 10000 SiO2.*.inp
run 50000

I wonder how to correct it?

Looking forward to your reply.

Liu Shuhui
Nanchang University

units metal
atom_style charge
boundary p p p

read_data SiO2.data

mass 1 28.0855
mass 2 15.9994

pair_style hybrid/overlay morse 9.0 comb
pair_coeff 1 1 morse 0.007695 2.0446 3.7598
pair_coeff 1 2 morse 1.99597 2.6518 1.628
pair_coeff 2 2 morse 0.23272 1.3731 3.791
pair_coeff * * comb ffield.comb Si O # It seem you overwrite the potential of Si-Si, Si-O, O-O with this line.

Asterisk mean it can be any number. In this case, * can be 1 or 2. So you have apply comb potential to Si-Si, Si-O, O-O. I am not sure you are applying comb to which atom, if you don’t want to apply it to all atom, this line is wrong.

Jocabi

Sorry but this is not correct. Pair_style comb must use “* *”.

COMB has more than just long range electrostatics so when you add Morse on top of COMB the resulting potential is not a reasonable one. If you want to add long range electrostatics on top of Morse, consider using coul/long.

Ray

Please note that ‘comb’ != ‘coul’. Axel