LAMMPS WWW Site - LAMMPS Documentation - LAMMPS Mailing List Archives
[lammps-users] VACF like white nosie
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[lammps-users] VACF like white nosie


From: "????" <1178408727@...1204...>
Date: Sat, 19 May 2018 03:42:49 +0800

Dear Lammps user

when I use compute vacf to calculate the methane, the output is like white noise as shown in the picture. 

"compute vacf  all  vacf 1 1 1 
fix 3 all ave/time 10 10 100 c_vacf[4] file vacf.dat"


Here is the main script:
units real
variable       T equal 95
variable       Pressure equal 100
variable       V equal vol
variable       dt equal 0.01
variable       p equal 400 # correlation length
variable       s equal 1 # sample interval
variable       d equal $p*$s # dump interval
variable       steps  equal 500000

# convert from LAMMPS real units to SI

variable kB equal 1.3806504e-23 # [J/K] Boltzmann
variable kCal2J equal 4186.0/6.02214e23
variable A2m equal 1.0e-10
variable fs2s equal 1.0e-15
variable       atm2Pa equal 101325.0

variable convertK equal ${kCal2J}*${kCal2J}/${fs2s}/${A2m}
variable convertV equal ${atm2Pa}*${atm2Pa}*${fs2s}*${A2m}*${A2m}*${A2m}


boundary p p p
atom_style full
read_data methane0.27.data

pair_style lj/cut/coul/cut 15
bond_style harmonic
angle_style harmonic
pair_modify mix geometric tail yes
special_bonds lj/coul 0.0 0.0 0.5
pair_coeff   1 1  0.066 3.5      # CT
pair_coeff   2 2  0.03  2.5      # HC
pair_coeff   1 2  0.044497191  3      # HC

# the remaining parameters are inferred from mixing.
bond_coeff   1   340.0   1.09    # CT-HC
angle_coeff  1    33.0   107.8     # HC-CT-HC
#bond_coeff   1   2845.12   1.09    # CT-HC
#angle_coeff  1    276.14 107.8     # HC-CT-HC

neighbor 1.5 bin 
neigh_modify every 10 delay 20 check yes
fix     1 all npt temp $T $T 100 drag 0.2  iso ${Pressure} ${Pressure} 1000
thermo_style custom step temp pe ke press vol density
velocity all create $T 432567 dist uniform
timestep       ${dt}
thermo         $d
run   100000
reset_timestep 0

compute vacf  all  vacf 1 1 1 
fix 3 all ave/time 10 10 100 c_vacf[4] file vacf.dat

run ${steps}
Any useful advice is appreciate.
best ragars!
cheng