Pressure is incorrect while simulation run

LAMMPS LAMMPS General Discussion
1

I am trying to calculate pressure in reduced unit for rho = 0.448 and T =0.05
Pressure supposed to come approximate to 0.01 but its coming 0.2.

Here my lammps script for silicon


units		metal

atom_style 	atomic
boundary	p p p


#variables
variable  tmp index 0.05
variable   rho1 index 0.489



variable       sigma index  2.0951 
variable       epsilon equal 2.1683

variable	dt index 0.005

variable rho equal  (8.0*${sigma}*${sigma}*${sigma}/${rho1})^(1.0/3.0)

#scaling factors

variable        tmpscale index 25161.7       	#temperature scale
variable        massKgAtom equal 4.659472e-26   #mass 
variable        tscale equal 7.66e-2 		#time scale
variable        pscale equal 3.77e5             #pressure scale in bars

#for outputing value in reduced unit

variable        temp equal temp/${tmpscale}
variable        pe equal pe/${epsilon}
variable        ke equal ke/${epsilon}
variable        etotal equal etotal/${epsilon}
variable        press equal press/${pscale}




variable t equal $(v_tmp*v_tmpscale)
variable 	a equal ${rho}

lattice  	custom ${a}  &
		a1 1.0 0.0 0.0 		&
		a2 0.0 1.0 0.0 		&
		a3 0.0 0.0 1.0 		&
		basis 0.0 0.0 0.0 	&
		basis 0.0 0.5 0.5       &
                basis 0.5 0.0 0.5       &
                basis 0.5 0.5 0.0       &
                basis 0.25 0.25 0.25    &
                basis 0.25 0.75 0.75    &
                basis 0.75 0.25 0.75    &
                basis 0.75 0.75 0.25
                
region 		box block 0 5 0 5 0 5
create_box	1 box


create_atoms    1 region box 

mass 		* 28.06
velocity        all create ${t} 5287287


pair_style      sw
pair_coeff      * * Si.sw Si 



thermo_style    custom step density temp pe press v_temp v_pe v_ke v_etotal v_press
thermo          10
fix             1 all nvt temp ${t} ${t} 0.1
timestep        0.005

variable	curstep equal step

fix             myData all print 1 "${curstep} $(v_temp) $(v_press) $(v_pe) $(v_ke) $(v_etotal)" screen no file Si_rho2.dat title "#Step Temp Pres PE KE TotlE"
dump 		1 all custom 10 silicon_rho0.489.xyz xu yu zu
neighbor        2.0 bin
neigh_modify    every 1 delay 0 check yes


run 	30000

Could you tell me whats wrong in it?

2

You could start by formatting your input code. It’s the </> button, it makes the world a better place.

3

thanks for telling me that

1 Like
4

I have complete trust in what LAMMPS computes in metal units, so the mistake must be in your conversions/computations. So the pressure is correct.