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Re: [lammps-users] Lennard-Jones 2D pressure changes with potential cut off

# Re: [lammps-users] Lennard-Jones 2D pressure changes with potential cut off

 From: Giacomo Fiorin Date: Thu, 10 Aug 2017 10:01:15 -0400

On Thu, Aug 10, 2017 at 6:57 AM, wrote:
Dear All,

Version of LAMMPS: 5 May 2012

Update.

I ran a 2D simulation of Lennard-Jones particles at various temperatures
and densities using an NVT ensemble and noted that the pressure (after
including long-range correction) increases with increasing cut off length
used for the potential.

pair potential used: lj/charmm/coul/charmm
Charge on particles: 0

The system contains 2500 particles and was run with periodic boundary
conditions. All data stated below are in Lennard-Jones units. I used the
_expression_ given below for long-range correction.

P_correction=12/5(pi)*(rho)^2*[(1/r_i)^10-5/4*(1/r_i)^4]

rho=density, T=temperature, P=pressure, delta P=uncertainty in pressure,
pi=3.14, r_i=inner cut-off radius used for potential, r_o=outer cut-off
radius used for potential.

T       rho     r_i     r_o     P       delta P
0.5     0.75    3.0     3.1     0.2936  0.0014
3.5     3.6     0.3065  0.0016
4.0     4.1     0.3216  0.0007
4.5     4.6     0.3230  0.0024

0.7     0.75    3.0     3.1     1.1724  0.0026
3.5     3.6     1.1874  0.0028
4.0     4.1     1.2020  0.0031
4.5     4.6     1.2037  0.0023

1.0     0.75    3.0     3.1     2.3817  0.0037
3.5     3.6     2.3951  0.0019
4.0     4.1     2.4063  0.0037
4.5     4.6     2.4116  0.0030

1.0     0.50    3.0     3.1     0.5510  0.0010
3.5     3.6     0.5589  0.0008
4.0     4.1     0.5648  0.0008
4.5     4.6     0.5658  0.0004

1.4     0.10    3.0     3.1     0.1386  0.0001
3.5     3.6     0.1390  0.0001
4.0     4.1     0.1391  0.0001
4.5     4.6     0.1392  0.0001

Regards,
Sindhana Selvi P.S.
Masters student (Physics)
Indian Institute of Science

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Giacomo Fiorin
Associate Professor of Research, Temple University, Philadelphia, PA
Contractor, National Institutes of Health, Bethesda, MD