Cooling glass melt with Reax - Temp randomly increases to 858000K

Dear all,

I am modeling a Na2O-Al2O3-SiO2 glass using reax. I melted it at 3000K for 300ps and now cooling it from 3000K to 300K at 1K/ps. At some timestep the temperature randomly increase to very high (this time) around 858472.83 K. I have encountered this problem multiple times. The system responds by blowing the box volume to 10^12. My usual solution is to restart from a certain timestep before the drastic temperature increase.

I have the input file and thermo output (two cases) below.

Could you please suggest me what might be a probably source of this kind of problem?

Thank you.

Sincerely,
Ruhil Dongol

Lammps input:

REAX potential for Soda-aluminosilicate glass system

units real
dimension 3
boundary p p p
atom_style charge
read_restart restart.3000K.NaAlSi2

pair_style reax/c NULL
pair_coeff * * ffield.reax.NaAlSi O Na Al Si
fix 99 all qeq/reax 1 0.0 10.0 1.0e-6 reax/c
neighbor 2.0 bin
neigh_modify delay 0 every 1 check yes
timestep 1
#dump 2 all xyz 1000 md.xyz
dump 1 all xyz 1000 traj.xyz
thermo 100
thermo_style custom step etotal temp press pe vol lx dt time

#------------------------------3000K-------------------------------
#print “Equilibration at 3000K”
#fix 1 all npt temp 3000 3000 100 iso 0 0 100
#restart 25000 3000K.*.restart
#timestep 0.5
#dump 3 all xyz 10000 traj.3000K
#run 600000
#unfix 1
#print “Equilibration Completed”
#write_restart restart.3000K.NaAlSi2

#-------------------------Melting-----------------------------------
print “Melting 3000k-300K at 1K/ps”
fix 1 all npt temp 3000 300 50 iso 0 0 50
timestep 0.5

restart 10000 restart..melt
dump 5 all xyz 10000 traj.melt
#dump d0 all image 100 dump.
.melt.png type type
run 5400000
unfix 1
print “Melting Completed”
write_restart restart.NaAlSi3

Thermo reading/output:

Case1:
step etot temp press pe vol lx dt time

2460600 -516796.43 2245.6627 -2918.6623 -543565.31 71810.109 41.565071 0.5 550300
2460700 -516810.5 2225.9414 6113.343 -543344.3 71849.176 41.572607 0.5 550350
2460800 -517384.99 2194.041 -6956.2063 -543538.53 71876.549 41.577886 0.5 550400
2460900 -517695.3 2192.95 2712.9382 -543835.83 71902.884 41.582963 0.5 550450
2461000 -517833.27 2200.5398 1525.3131 -544064.28 71936.625 41.589467 0.5 550500
2461100 -518161.07 2193.9419 -6306.8719 -544313.43 71977.57 41.597356 0.5 550550

2461200 -518606.78 2148.6497 1556.6849 -544219.24 71952.504 41.592527 0.5 550600

2461300 -518207.19 2162.2473 -446.71595 -543981.73 71983.155 41.598432 0.5 550650
2461400 9788629.4 858472.83 3923863.3 -444589.45 113652.39 48.438742 0.5 550700
2461500 -442559.78 2652.8328 -103235.04 -474182.24 126135 50.150877 0.5 550750
2461600 -488228.04 1060.375 -84217.194 -500867.98 122486.03 49.662532 0.5 550800
2461700 -500417.12 1067.4638 -65893.241 -513141.57 119754.88 49.290634 0.5 550850
2461800 -497819.47 1658.0389 -50244.209 -517583.73 117730.98 49.011379 0.5 550900

2461900 -481141.1 2842.7184 -39374.57 -515027.04 116232.49 48.802549 0.5 550950
2462000 -476250.22 2932.3587 -28629.475 -511204.7 115145.92 48.650001 0.5 551000
2462100 -489734.33 2128.4659 -24467.127 -515106.2 114292.25 48.529475 0.5 551050

Case2:
step etot temp press pe vol lx dt time

516700 -501770.1 2751.1992 706.35367 -534565.11 66873.913 40.589987 0.5 258350
516800 -501795.62 2782.0923 -1212.1971 -534958.89 67013.177 40.618143 0.5 258400
516900 -88122.552 36096.1 121293.68 -518397.42 73822.423 41.949755 0.5 258450
517000 4778.9817 40208.063 109909.55 -474511.56 94643.053 45.571807 0.5 258500
517100 -200162.4 21364.148 20970.496 -454828.59 112682.93 48.300621 0.5 258550
517200 -315093.18 12175.092 -668.38778 -460223.44 118440.23 49.109602 0.5 258600
517300 -370458.44 8050.4153 -1128.8203 -466421.48 119166.72 49.209807 0.5 258650
517400 3067504 284912.75 515257.45 -328729.87 265507.6 64.272568 0.5 258700
517500 68426.682 38322.615 42931.928 -388388.83 396377.94 73.457559 0.5 258750
517600 -273185.95 11474.469 9682.6288 -409964.6 455757.18 76.956358 0.5 258800
517700 -355957.06 5256.3104 3078.69 -418613.64 489427.73 78.806648 0.5 258850
.

.
.

590600 -457699.54 2722.0326 7.4308469e-05 -490146.87 3.1574755e+12 14670.559 0.5 295300
590700 -457630.16 2751.4618 7.4513749e-06 -490428.3 3.2181682e+12 14763.962 0.5 295350
590800 -457803.34 2741.3841 8.5638483e-05 -490481.35 3.2762249e+12 14852.215 0.5 295400
590900 -458038.13 2707.7845 -4.8381749e-05 -490315.62 3.3332434e+12 14937.881 0.5 295450
591000 -458297 2682.2313 -9.4893858e-05 -490269.9 3.3810233e+12 15008.918 0.5 295500

Dear all,

I am modeling a Na2O-Al2O3-SiO2 glass using reax. I melted it at 3000K for
300ps and now cooling it from 3000K to 300K at 1K/ps. At some timestep the
temperature randomly increase to very high (this time) around 858472.83 K.
I have encountered this problem multiple times. The system responds by
blowing the box volume to 10^12. My usual solution is to restart from a
certain timestep before the drastic temperature increase.

I have the input file and thermo output (two cases) below.

Could you please suggest me what might be a probably source of this kind of
problem?

bad choice of time step?

axel.