[lammps-users] Lattice constant of High Entropy Alloy


I am trying to characterize main thermodynamic properties of a high entropy alloy with a meam potential. I am mainly interested in the definition of the system pe, avg lattice constant and rdf @ 300 K, for different alloy compositions. I am running a simulation like this:

units metal

boundary p p p

atom_style atomic

atom_modify map array

lattice fcc 3.68

region whole block 0 40 0 40 0 40

create_box 5 whole

lattice fcc 3.68 orient x 1 0 0 orient y 0 1 0 orient z 0 0 1

create_atoms 1 region whole

variable fMn equal 0.20

variable fNi equal (1-${fMn})/4

variable fCr equal (1-${fMn})/4

variable fFe equal (1-${fMn})/4

set type 1 type/fraction 2 $((v_fNi+v_fCr+v_fFe+v_fMn)) 5467

set type 2 type/fraction 3 $((v_fCr+v_fFe+v_fMn)/(v_fNi+v_fCr+v_fFe+v_fMn)) 6556

set type 3 type/fraction 4 $((v_fFe+v_fMn)/(v_fCr+v_fFe+v_fMn)) 7754

set type 4 type/fraction 5 $(v_fMn/(v_fFe+v_fMn)) 8574

pair_style meam/c

pair_coeff * * library.meam Co Ni Cr Fe Mn CoNiCrFeMn.meam Co Ni Cr Fe Mn

compute csym all centro/atom bcc

compute myRDF all rdf 500 1 1 2 2 cutoff 4.8

thermo 1000

thermo_style custom step pe lx ly lz press pxx pyy pzz

velocity all create 300.0 548494 rot yes dist gaussian

fix 1 all npt temp 300 300 0.1 iso 1 1 1

run 50000

minimize 1e-10 1e-10 10000 10000

unfix 1

reset_timestep 0

fix 4 all ave/time 100 1 100 c_myRDF[*] file my_rdf.txt mode vector

run 100

unfix 4

variable mype equal pe

variable real_ao equal “lx/40”

print ${mype} append PE.data

print ${real_ao} append lattice.data

As far as I know, pe should stabilize around a certain value while pressure should stabilize around 0 (or 1 in my case), in order to consider a system relaxed. However, while my pe does stabilize, my pressure starts at about -1e5 bar at the first timestep and then fluctuates between -200 and 100 bar, it goes like this . Is it sufficient to consider the system stable or there is something wrong with the model? Thank you.



please see the mailing list archives on previous discussions about pressure fluctuations.