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[lammps-users] pressure equilibrium
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[lammps-users] pressure equilibrium


From: Hossein Geraili <geraili.hsn@...24...>
Date: Mon, 4 Sep 2017 08:09:04 +0430

Dear Lammps users,
after a long period of time of simulation now I find out maybe my input file would not be correct because I would always compare the volume of lammps pVT results, but now, I find out the pressure is not well- fitted.
I added some new codes to reach a better result for pressure, but I am just getting errors and I am not sure if they are going to work or my input file is correct at all. 
I appreciate any advice.
my input file:
units       real
dimension 3
boundary p p p
atom_style full

#######################################################
#                                                     #
#           Setting & atom defination                 #
#                                                     #
#######################################################    

bond_style   harmonic
angle_style   harmonic
dihedral_style opls
improper_style  cvff
pair_style lj/cut/coul/long  11
pair_modify     mix geometric tail yes
kspace_style pppm 1.0e-4
read_data       ionicdata.data
neighbor        2.0  bin
neigh_modify delay 2 every 1 check yes

#######################################################
#                                                     #
#                Simulation for 1 ns                  #
#                                                     #
####################################################### 


velocity all create 350 4928459  rot yes dist gaussian
group 1 type 1 2 3 4 5 6 10 11 12 13 14 15 16
group 2 type 7 8 9 17

variable etotal equal etotal 
variable ke equal ke
variable pe  equal pe

fix         1 all nve/limit 0.01

fix         2 all box/relax iso 0.0 vmax 0.001

run 100000
unfix 1
unfix  2
fix         3 all press/berendsen iso 1184 1184 100.0

run     50000   
unfix    3
fix         4 all ave/time 100 1000 100000 c_thermo_press file pressure.txt
fix         5 all ave/time 100 1000 100000 c_thermo_temp  file Temperature.txt

timestep 1
thermo 100
thermo_style    custom step temp etotal ke pe press vol enthalpy lx ly lz pxx pyy pzz ecoul elong evdwl epair cpu

minimize    1.0e-6 1.0e-8  1000  100000

fix         6 all  nvt temp 350 350  10.0
run 1000000

the bold ones are new. I want to reach to the 1184 atm pressure in press/brendsen.

before I add these bold codes the pressure results which have a great deviation from exp. data were:
# TimeStep c_thermo_press
200000 2195.97
300000 2210.41
400000 2086.78
500000 2095.61
600000 1940.03
700000 1958.81
800000 2014.47
900000 1974.02
1000000 1944.95
they fluctuate largely and are not really correct compare to exp. data.
thanks

--
Hosein Geraili Daronkola
M.Sc.Graduated of physical chemistry
Physical Chemistry,
Department of Chemistry,
Sharif University of Technology.
geraili_hosein@...7110...



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