Dear Altruist,
I am trying to work on finding out the pressure vs density relationship for water molecules. Here, I used a data file for water molecules (containing 1500 molecules and density of 1000Kg/m3). The potential forcefield was chosen to lj interaction with coulombic range. But, when I run the simulation with nvt, then I found that pressure was changing, but density was remained constant. Also, the temperature was not found constant at 300K. Would you like to help how could I get good pressure vs density curve from this input script? Where is the problem in this input script? I really need help in this case as I am new to learning simulation.
Sincerely,
Akash Talapatra
MS student, Virginia Tech
#Input script
units real
atom_style full
boundary p p p
read_data water(1000).data
replicate 1 1 1
variable dt equal dt
variable ext_temp equal 300
mass 1 15.9994
mass 2 1.008
variable Tdamp equal 100.0*${dt}
pair_style lj/cut/coul/long 9.0 9.0
pair_modify tail yes
kspace_style pppm 1.0e-4
pair_coeff 1 1 0.15539421659476232 3.16555789
pair_coeff * 2 0.0000 0.0000
bond_style harmonic
angle_style harmonic
dihedral_style none
improper_style none
bond_coeff 1 5000.00 1.000
angle_coeff 1 500.0 109.47
#Create initial velocity distribution
velocity all create ${ext_temp} 432567 dist uniform
#Reset the time step counter
reset_timestep 0
#SHAKE Parameters to preserve bondlengths
fix 1 all shake 0.0001 20 0 b 1 a 1
#Ensemble set-up: NVT ensemble, thermostatted by Nose-Hoover a chained thermostat, set at temperature ext_temp
fix 2 all nvt temp {ext_temp} {ext_temp} {Tdamp}
#timestep 0.5
#Output Style
variable Nevery equal 20
variable Nrepeat equal 50
variable Nfreq equal {Nevery}*{Nrepeat}
variable PotentialEnergy equal epair
variable Pressure equal press
variable Temperature equal temp
variable Density equal density
fix 3 all ave/time {Nevery} {Nrepeat} ${Nfreq} v_Temperature v_PotentialEnergy v_Pressure file ave.dens_1000kgm3.out format %.8g
dump st all custom 100 dump.lammpstrj id type x y z
thermo 1000
thermo_style custom step temp density epair press
#Run it!
run 60000
#Outputs
Step Temp Density E_pair Press
0 450.05002 1.0000059 -9823.1202 15649.381
1000 297.78229 1.0000059 -16549.086 -681.74344
2000 296.56455 1.0000059 -16723.059 386.22762
3000 297.68996 1.0000059 -16781.364 462.93578
4000 297.96643 1.0000059 -16689.808 531.10791
5000 300.97047 1.0000059 -16693.015 -419.22291
6000 302.47401 1.0000059 -16838.386 131.47509
7000 298.78537 1.0000059 -16798.136 124.73786
8000 296.31094 1.0000059 -16759.38 80.834287
9000 296.9679 1.0000059 -16783.12 -302.43309
10000 305.12358 1.0000059 -16772.815 152.49701
11000 301.0554 1.0000059 -16749.773 81.422811
12000 295.94107 1.0000059 -16727.506 -111.04608
13000 293.41613 1.0000059 -16711.442 -543.91158
14000 303.78818 1.0000059 -16728.467 -337.74409
15000 302.84376 1.0000059 -16702.389 -70.632047
16000 301.97565 1.0000059 -16729.029 494.58834
17000 304.80025 1.0000059 -16698.838 599.31846
18000 298.86411 1.0000059 -16781.149 405.64783
19000 303.71063 1.0000059 -16716.012 89.099738
20000 303.65877 1.0000059 -16814.3 -195.30294
21000 306.9728 1.0000059 -16768.676 146.53848
22000 305.16509 1.0000059 -16767.722 -330.66466
23000 311.26889 1.0000059 -16642.254 135.18624
24000 303.30852 1.0000059 -16807.744 67.820395
25000 310.80295 1.0000059 -16790.206 868.86566
26000 300.21857 1.0000059 -16601.377 20.002035
27000 297.02305 1.0000059 -16534.666 371.72524
28000 293.81809 1.0000059 -16635.014 -136.15918
29000 295.67957 1.0000059 -16731.441 493.57746
30000 293.33474 1.0000059 -16693.485 -248.27554
31000 302.17025 1.0000059 -16748.443 331.17401
32000 298.32418 1.0000059 -16629.347 161.55044
33000 302.9666 1.0000059 -16681.582 -63.021334
34000 300.54374 1.0000059 -16817.865 -67.415523
35000 305.49678 1.0000059 -16828.5 62.712364
36000 296.90462 1.0000059 -16726.777 235.69704
37000 299.64712 1.0000059 -16855.124 314.17953
38000 289.29864 1.0000059 -16753.823 67.643625
39000 298.25035 1.0000059 -16696.994 376.87236
40000 289.85982 1.0000059 -16814.177 327.49061
41000 293.26169 1.0000059 -16689.921 379.2272
42000 296.04682 1.0000059 -16816.177 -602.71629
43000 307.06156 1.0000059 -16735.833 187.46977
44000 303.15135 1.0000059 -16829.363 417.48567
45000 304.24218 1.0000059 -16712.185 -435.83222
46000 296.84282 1.0000059 -16734.585 138.69402
47000 295.51977 1.0000059 -16744.186 231.43523
48000 296.63454 1.0000059 -16698.147 -750.76937
49000 303.13461 1.0000059 -16703.513 -369.22278
50000 292.71464 1.0000059 -16686.245 433.57969
51000 301.67637 1.0000059 -16617.251 332.72543
52000 303.97802 1.0000059 -16722.127 681.26606
53000 297.76704 1.0000059 -16750.351 -337.23038
54000 303.08515 1.0000059 -16722.017 -236.79643
55000 298.90843 1.0000059 -16777.384 193.38446
56000 293.29691 1.0000059 -16776.642 -55.164427
57000 302.65835 1.0000059 -16727.362 67.004336
58000 296.20336 1.0000059 -16742.291 -63.663928
59000 301.9545 1.0000059 -16698.477 -116.76893
60000 304.42752 1.0000059 -16597.112 -537.5654