make SiO2-spp amorphous equilibrated at the given temperature

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1

Dear colleagues! I have tried to calculate thermal conductivity of amorphous silicon oxide - free standing layer - using fix heat (NEMD). Nevertheless, it was impossible to prepare the sample in equilibrium at the given temperature (e.g. 500 K) by means of “fix all nve” & “fix all qeq/comb”. If no temperature control is applied, the sample starts to heating without any reason. My script is :

make SiO2 amorphous equilibrated at the given temperature

units metal
atom_style charge
boundary s p p

read_data data.silica # “data.silica” is from the LAMMPS-Mail-List

mass 1 28.086
group type1 type 1
compute charge1 type1 property/atom q
compute q1 type1 reduce ave c_charge1
mass 2 16.00
group type2 type 2
compute charge2 type2 property/atom q
compute q2 type2 reduce ave c_charge2

pair_style comb
pair_coeff * * ffield.comb Si O
neighbor 0.5 bin
neigh_modify every 20 delay 0 check no

timestep 0.00020

thermo_style custom step temp etotal pe evdwl ecoul press vol c_q1 c_q2

fix 1 all nve
fix 2 all qeq/comb 1 0.0001

velocity all create 10.0 277387

thermo 10
run 1000

2

Ray can comment on the use of COMB for this. You don't
need to use fix heat. Just use a thermostat to heat your
sample beyond the melting point.

Steve

3

To equilibrate a sample at a certain temperature, fix nve and fix
qeq/comb are not enough. Like Steve said, you need a thermostat.

Your script looks alright. If you are still having problems, check
your amorphous structure. Characterize and verify it. Certainly you
can not write a paper with a structure "obtained from a random mailing
list from a random person".

Ray