Dear Axel,
Thank you very much for your prompt response.
I am observing the following thing while this change occurs in temperature and pressure
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The water molecules, which forms droplet (collection of few molecules) get frozen however the vapor molecules move randomly but get arrested once associate with those droplets.
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When I am running without fix gcmc, the simulation goes well with NVT simulation
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When I am using 0.1 fs time step, it occurs around 16500 step however around 10500 step in the case of 1 time step.
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I am running the simulation at 300K which is below the boiling point. I am interested to find out the equilibrium chemical potential at 300K for liquid vapor coexistence.
I just wanted to mention that when we use pressure command in fix gcmc (please see the script below), the chemical potential would be ignored therefore i have run the another simulation without pressure command but the issue has not been resolved.
Dear Simon,
Yes i have used the compute_modify dynamic/dof. Please let me know if you find someting wrong in the script below.
Input script:
variable vol equal 8000000
units real
atom_style full
boundary p p p
region 1 block 0 200 0 200 0 200
read_data water_mW.data
neighbor 2 bin
neigh_modify every 1 delay 0 check yes
velocity all create 300.0 54654
pair_style sw
pair_coeff * * system.in.sw mW
group 1 region 1
mass 1 18.015
fix 1 all momentum 1 linear 1 1 1
timestep 1
min_style cg
minimize 1e-20 1e-20 10000 10000
min_style sd
minimize 1e-40 1e-40 10000 10000
reset_timestep 0
print “================================================”
print “GCMD dynamics for 2000ps”
print “================================================”
fix gcmc1 1 gcmc 1000 100 0 1 99999 300 -10.4 0.5 region 1 pressure 0.1 fugacity_coeff 0.95 group 1 grouptype 1 1 tfac_insert 1
compute t1 1 temp/region 1
compute_modify t1 dynamic/dof yes
variable 1 atom “type==1”
group 3 dynamic all region 1 every 1
compute p1 3 stress/atom t1
compute p1rd3 3 reduce sum c_p1[1] c_p1[2] c_p1[3]
variable press1 equal (-(c_p1rd3[1]+c_p1rd3[2]+c_p1rd3[3])/(3*(vol/3)))*0.101325
fix p1 3 ave/time 1 100 100 v_press1 ave running start 20000 title1 “Average Press[MPa]” file avep0.1_t0.1fs.txt
variable p1ave equal f_p1
variable 3 equal count(3)
thermo_style custom step temp press pe ke density atoms v_3 c_t1 v_press1 v_p1ave
thermo 1000
thermo_modify lost ignore
dump 1 all atom 100000 GCMD_only.dump
run 2000000
unfix gcmc1
undump 1
unfix p1
print “==================================================================”
print “NVT simulation with GCMD”
print “=================================================================”
reset_timestep 0
timestep 0.1
fix gcmc1 1 gcmc 1 20 0 1 99999 300 -10.4 0.5 region 1 pressure 0.1 fugacity_coeff 0.95 group 1 grouptype 1 1 tfac_insert 1
fix 5 1 nvt temp 300.0 300.0 100.0
compute t3 1 temp/region 1
compute_modify t3 dynamic/dof yes
compute p3 3 stress/atom t3
compute p3rd3 3 reduce sum c_p3[1] c_p3[2] c_p3[3]
variable press3 equal (-(c_p3rd3[1]+c_p3rd3[2]+c_p3rd3[3])/(3*(vol/3)))*0.101325
fix p5 3 ave/time 1 100 100 v_press3 ave running start 30000 title1 “Average Press[MPa]” file avep0.1nvt_0.1fs.txt
variable p5ave equal f_p5
thermo_style custom step temp press pe ke density atoms v_3 c_t3 v_press3
thermo 100
thermo_modify lost ignore
dump 3 all atom 1000 GCMD_NVT.dump
run 1000000
unfix 5
Thanks,
Moid