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lammps/examples/MC/in.mc
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in.mc
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# Monte Carlo relaxation of perturbed 2d hex lattice
# set these parameters
# make sure neigh skin > 2*deltamove
variable iter loop 3000 # number of Monte Carlo moves
variable deltaperturb equal 0.2 # max size of initial perturbation per dim
variable deltamove equal 0.1 # max size of MC move in one dimension
variable density equal 1.0 # reduced LJ density of atoms on lattice
variable kT equal 0.05 # effective T in Boltzmann factor
variable seed equal 582783 # RNG seed
# problem setup
units lj
atom_style atomic
atom_modify map array sort 0 0.0
dimension 2
lattice hex ${density}
region box block 0 10 0 5 -0.5 0.5
create_box 1 box
create_atoms 1 box
mass 1 1.0
pair_style lj/cut 2.5
pair_coeff 1 1 1.0 1.0 2.5
pair_modify shift yes
neighbor 0.3 bin
neigh_modify delay 0 every 1 check yes
variable e equal pe
# run 0 to get energy of perfect lattice
# emin = minimum energy
run 0
variable emin equal $e
# disorder the system
# estart = initial energy
variable x atom x+v_deltaperturb*random(-1.0,1.0,${seed})
variable y atom y+v_deltaperturb*random(-1.0,1.0,${seed})
set group all x v_x
set group all y v_y
#dump 1 all atom 25 dump.mc
#dump 2 all image 25 image.*.jpg type type &
# zoom 1.6 adiam 1.0
#dump_modify 2 pad 5
#dump 3 all movie 25 movie.mpg type type &
# zoom 1.6 adiam 1.0
#dump_modify 3 pad 5
variable elast equal $e
thermo_style custom step v_emin v_elast pe
run 0
variable estart equal $e
variable elast equal $e
# loop over Monte Carlo moves
variable naccept equal 0
variable increment equal v_naccept+1
variable irandom equal floor(atoms*random(0.0,1.0,${seed})+1)
variable rn equal random(0.0,1.0,${seed})
variable boltzfactor equal "exp(atoms*(v_elast - v_e) / v_kT)"
variable xnew equal x[v_i]+v_deltamove*random(-1.0,1.0,${seed})
variable ynew equal y[v_i]+v_deltamove*random(-1.0,1.0,${seed})
variable xi equal x[v_i]
variable yi equal y[v_i]
label loop
variable i equal ${irandom}
variable x0 equal ${xi}
variable y0 equal ${yi}
set atom $i x ${xnew}
set atom $i y ${ynew}
run 1 pre no post no
if "$e <= ${elast}" then &
"variable elast equal $e" &
"variable naccept equal ${increment}" &
elif "${rn} <= ${boltzfactor}" &
"variable elast equal $e" &
"variable naccept equal ${increment}" &
else &
"set atom $i x ${x0}" &
"set atom $i y ${y0}"
next iter
jump SELF loop
# final energy and stats
variable nb equal nbuild
variable nbuild equal ${nb}
run 0
print "MC stats:"
print " starting energy = ${estart}"
print " final energy = $e"
print " minimum energy of perfect lattice = ${emin}"
print " accepted MC moves = ${naccept}"
print " neighbor list rebuilds = ${nbuild}"
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