Sudden decrease of molecular velocity

LAMMPS LAMMPS Beginners
1

Dear all,
I am a beginner. I used the deposition command to give the molecular speed of CF4, but after running for a period of time, the molecular speed gradually decreases, and even cannot reach the SiO2 substrate. I am attaching three files, input files and a data files. Because it is reaxff, I deleted the bond in the molecular template.
I would appreciate any help.
Best regards,
#--------------------------Initialize -----------------------------------
dimension 3
units real
atom_style full
boundary p p f
timestep 0.25
#--------------------------Atom Defination-------------------------------
read_data data.SiO2full extra/atom/types 2
mass 1 15.999 # O
mass 2 28.085 # Si
mass 3 18.998 # F
mass 4 12.107 # C
#--------------------------Define Interatomic Potential------------------
pair_style reax/c NULL
pair_coeff * * CHONSSiNaFZr.ff O Si F C
neighbor 0.5 bin
neigh_modify every 10 delay 0 check no
#-------------------------- Matrix Construction -------------------------
region zlo block INF INF INF INF INF 7 units box
region zhi block INF INF INF INF 7 INF units box
group zlow region zlo
group zhig region zhi
group jidi type 1 2
group add type 3 4
region slab block 3 13 3 13 45 55
#group CF4 id 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276
#--------------------------Run Minimization-------------------------------
fix qeq all qeq/reax 1 0.0 10.0 1e-6 reaxff
minimize 1e-25 1e-25 5000 10000
thermo_modify lost ignore flush yes
fix 1 jidi nvt temp 308.0 308.0 100.0
run 1000
unfix 1
reset_timestep 0
velocity zlow set 0.0 0.0 0.0
#velocity CF4 set 0.0 0.0 -0.6
fix zlowforce zlow setforce 0.0 0.0 0.0
#-------------------------- Temp Start ----------------------------------
molecule CF4 molecule.CF4
fix 2 add nve
fix 3 zhig nve
fix 4 all temp/berendsen 308.0 308.0 100.0
fix depoMole add deposit 10 0 1000 12345 region slab near 1.0 mol CF4 vz -0.1 -0.1 units box
thermo 1000
thermo_modify lost ignore flush yes
reset_atom_ids
dump 1 all atom 50 dump.reax.SiO2Long
dump 2 all custom 50 dump.reax.SiO2Long.lammpstrj id mol type q x y z
fix 5 all reaxff/bonds 50 bonds.reaxff
run 10000

LAMMPS data file written by OVITO Basic 3.7.6

5 atoms

Coords

1 1.659 2.291 5.0
2 1.209 2.928 6.102
3 1.209 1.018 5.0
4 3.009 2.291 5.0
5 1.209 2.928 4.102

Types

1 4
2 3
3 3
4 3
5 3

Charges

1 4
2 -1
3 -1
4 -1
5 -1

2

You are applying a thermostat to the group “all”. That includes the deposited atoms, but their motion toward the substrate raises the total kinetic energy and thus total temperature. As a consequence their velocity is modified. This is not what you want. Thus you should apply the thermostat only to the substrate.

3

Thank you very much！My problem has been solved. Thank you for your reply, which is very important for me as a beginner.