Dear lammps users,

I am trying to estimate the pressure values for liquid Ar at a density of 1.3954 g/cc. This has been done by putting 2048 atoms of Ar in 46A cubic box.

*Number of atoms = 2048*

*Mass of Argon = 39.948 gm/mole*

*Na = 6.022*10^23*

*Box Length = 46 A*

*angstrom to cm = 10^-8*

density = (Number of atoms)*(Mass of Argon/Na)/(Box Length *angstrom to cm)^3

Putting in all the variables from above, we get,

*density = 2048*(39.948/(6.022 10^23))/((4610^-8)^3)*

*density = 1.3954 gm/cc*I *am using the L-J parameters by "John A. White “Lennard-Jones as a model for argon and test of extended renormalization group calculations”, Journal of Chemical Physics 111 pp. 9352-9356 (1999"*

where they specify value of epsilon/Kb = 125.7 K and sigma = 0.3345 nm. These values when converted to corresponding lammps real units become epsilon = 250 and sigma = 3.34 A.

The cutoff in units real then becomes 2.5*sigma which is 8.34 A.

So my pair coefficient are** pair_coeff * * 250 3.34 8.34**

*The value of pressure at 47 K should be close to 10 Pa, but I am getting -10^7 atm.*

I do not know what error I am committing here. Is **units real option a problem here Should I do the calculation in units LJ.**

I am attaching my data file and input file along with this email. I am using *Nov, 2016 version of the lammps stable release.*

Please, provide your suggestions.

P.S. I am using units real and hence my coordinates are in angstrom.

Thanks,

Ankit

data.ar_2048 (91.5 KB)

in.test (1.38 KB)