gold sputtering substrate massive temp spike


I am wondering if anyone has any theories as to why I am observing an odd trend in my temperature profile during deposition. Below is the script. I have run this exact same script using a silver potential with no issue. The script works at low energies, but there is a massive temperature spike at the speed below that is not observed for silver. Could it be an issue with the potential? Seems odd to me as it works very well for the low energy simulations.

surface sputtering demo

------------------------ INITIALIZATION ----------------------------

dimension variables

box length in x and y

variable len index 15

height of layer

variable hgt index 10

delta between insert area and box

variable len0 index 0.1

full length minus delta

variable len1 equal {len}-{len0}

half length

variable len2 equal ${len}*0.5

#simulation set up

units real
atom_style full
boundary p p f
lattice fcc 4.07
region box block 0.0 {len} 0.0 {len} -1.0 20 units lattice

particle density in z-direction is inhomogeneous:

only do domain decomposition in x- and y-direction

processors * * 1

------------------------ regions and atom types ----------------------------

two atom types: surface and sputter atoms

create_box 2 box
region layer block 0.0 {len} 0.0 {len} 0.0 ${hgt}
create_atoms 2 region layer

mass 1 15.99
mass 2 196.967

region fixed block INF INF INF INF 0.0 0.1
group fixed region fixed

group mobile subtract all fixed

region simulation block 0.2 14.8 0.2 14.8 0.3 10
group simulation region simulation

group bath subtract all simulation fixed

reaxff force field

pair_style reax/c NULL checkqeq yes
pair_coeff * * AuCSOH.ff O Au
fix 1 all qeq/reax 1 0.0 10.0 1.0e-6 reax/c

neigh_modify delay 0

minimize 1.0e-5 1.0e-8 1000 10000

------------------------ equilibration----------------------------

reset_timestep 0
timestep 0.5
velocity mobile create 200 87287

use the temperature of the mobile layer atoms as reference

compute stemp simulation temp
compute pe all pe/atom
compute btemp bath temp
compute mtemp mobile temp

fix 2 mobile nve
fix 3 simulation langevin 200 200 50 982434
fix 4 bath langevin 200 200 50 982434

fix_modify 3 temp mtemp
thermo 100
thermo_style custom step atoms temp etotal c_btemp
thermo_modify temp mtemp

dump 1 all custom 100 md.dump id type x y z c_pe

minimal equilibration

run 1000

------------------------ insert ----------------------------

define region for inserting particles

region obox block 3.75 11.25 3.75 11.25 18 22 units lattice
region insert intersect 2 box obox

define group of inserted particles

group insert region insert
group insert type 1

deposit particles regularly into insert volume

fix 5 insert deposit 100 1 400 54321 region insert vz -.0469 -.0469
neigh_modify every 1 delay 0 check yes

group insert region insert
group insert type 1

time integrate inserted particles

fix 6 insert nve

remove thermostat on simulation atoms

unfix 3
#unfix 4

thermo_style custom step atomstemp pe etotal c_btemp c_stemp
thermo_modify temp mtemp

fix 7 all reax/c/species 10 10 100 species.out

handling of atoms the get bounced back from surface or sputtered off the surface

thermo_modify lost ignore

restart 1000 damage.*.restart

run 45000

The temp profile looks like:

Have you visualized or analyzed the system around the time the spike
occurs? Are 2 atoms getting very close together? The compute pair/local
command can monitor the distances between all pairs of atoms.
Use its output with compute reduce to find the min distance.