Hi dear whom it may concern

I am doing a coarse-grained model of diffusion of nanoparticles in fluid. I use Bronian style with nvt and langevin. The problem is that when I increase the dynamic viscosity(DV) in pair_brownian command, the temperature increase greatly, much more than what I set via fix command.

Blow is my script:

units nano

atom_style sphere

dimension 3

boundary p p p

newton offlattice sc 10

lattice command defines the type of box, sc means simple cube, the number after sc is scale factor. For units lj, the length of box cubed times scale factor euqal to 1.

region box block 0 48 0 48 0 48 units lattice

region case block 19 28 19 28 19 28 units latticecreate_box 1 box

create_atoms 1 random 1000 20190714 caseset atom 1 diameter 5

set atom 1 density 0.0015neighbor 10 bin

neigh_modify every 1 delay 0 check yes page 10000 one 1000pair_style brownian/poly 0 0 1 5 10 310 20200514

pair_coeff * *compute rot all temp/sphere

compute kte all ke

compute pec all pe

compute pre all pressure rot

compute kre all erotate/sphere

compute angularvelocity all property/atom omegax omegay omegaz

compute shape all property/atom radius diameter

compute Temperature all tempvelocity all create 298 20200525 dist gaussian loop geom

run 0

velocity all scale 298.0variable step equal step

variable pe equal pe

variable ke equal ke

variable Total_energy equal etotal

variable Pressure equal press

variable Volume equal vol

variable Temperature equal temp#calculate diffusion coefficient

compute 2 all vacf

fix 5 all vector 1 c_2[1]

variable Diff equal dt*trap(f_5)

timestep 0.002

fix 2 all print 2000 “{step} {pe} {ke} {Total_energy} {Pressure} {Volume} {Temperature} {Diff}” file test.txt screen yes

dump 2 all custom 2000 0731.dump id type x y zfix 1 all nvt temp 310 310 50 drag 1

thermo_style custom step pe ke etotal press vol temp v_Diff

thermo_modify lost ignorerun 3000000

when I change pair_style brownian/poly 0 0 0 5 10 310 20200514 to **pair_style brownian/poly 1 0 0 5 10 310 20200514,**

the temperature increase from 310K (which is desired) to over 60000K,

How should I do to make the temp stay at 310K with changing the DV?

and tbh when I include Fast Lubrication Dynamics effects, the temperature change from 1000K to about 550K, why does that happen?

Thanks in advance!! Looking for your reply!