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[lammps-users] ethane equilibrium question
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[lammps-users] ethane equilibrium question


From: 陈懿楠 <breadcyn@...127...>
Date: Mon, 16 Apr 2018 17:50:38 +0800 (CST)

I want to do basic equilibrium simulation of ethane and compare my results with experimental or theoretical thermodynamic properties. But my results cannot match the experimental data well. 
For example, when pressure=0.5Mpa, temperature=300K, the density of ethane should be 6.26kg/m3, but my result is about 5.6kg/m3; when pressure=0.1Mpa, temperature=300K, the density of ethane should be 1.2144kg/m3, but my result is about 1.11kg/m3.  
How to do simple gas equilibrium simulation to get those correct thermodynamic properties like density? Is there any example I can refer to? My input file and molecule template are shown below:

Input file:
# ethane Equilibration

log log.eth
units real
molecule ETH c2h6.data 
#atom_style template ETH
atom_style full
bond_style harmonic



boundary p p p 

lattice fcc 54.49
region box block 0 10 0 10 0 10
create_box 1 box bond/types 1 extra/bond/per/atom 1


mass 1 15.035

create_atoms 0 box mol ETH 19871010  
#create_atoms 0 random 540 1111 NULL mol ETH 19871010 


velocity all create 300 482748

pair_style lj/cut 14.0
pair_coeff 1 1 0.1946 3.750
bond_coeff 1 95.806 1.54
special_bonds lj 0.0 0.0 0.0

minimize 1.0e-5 1.0e-7 1000 10000


fix   fxnpt all npt temp 300.00 300.00 100.0 iso 4.98 4.98 1000

dump id all atom 500 dump.Equeth.lammpstrj


timestep 1.0
thermo_style custom step temp press etotal density vol
thermo 500
run   2000000



molecule template file:
LAMMPS Description           

2 atoms         
1 bonds                
0 angles               
0 dihedrals
0 impropers


Coords

1 -0.77 0.0 0.0
2 0.77 0.0 0.0   


Types

1 1
2 1

Charges

1 0.0
2 0.0

Bonds

1 1 1 2

Special Bond Counts

1 1 0 0
2 1 0 0

Special Bonds

1 2 
2 1 




Thank you!!!


 

Attachment: eth.in
Description: Binary data

Attachment: c2h6.data
Description: Binary data