Thank you so much for the prompt reply. Really sorry for not getting back to you earlier, I was down with fever and cough for the past week. I will try and provide more information about my simulation here.
** I am attaching an input script and logfile from a simulation: 2000 nitrogen molecules in a box at 10 bar and 300K.
** And yes, I am using NVE
** For this case, the simulation domain has an area of cross-section of 5 nm * 5 nm and a length of 340 nm.
** I do run simulations for a long time. Each 0.1 ns corresponds to 50,000 steps run. That way I run till 20 ns and observe no change in the plots. So that’s a total of 50,000 * 20 steps.
Problem / Doubt:
** My problem still is that when I plot the V-rms from MD I get around 750 m/s whereas kinetic theory assuming 3 Degree of Freedom (DOF) gives just 550 m/s. This is at 300K.
** I don’t get this discrepancy when I deal with Helium with is mono-atomic and perfectly spherical. I get really good agreement of RMS with kinetic theory. Now helium can only have 3 DOF.
----- Here are my questions:
** when I dump vx, vy and vz from lammps, are they only translational components or they have a contribution from rotational components as well.
** 300-350K is very low for vibrational modes to be activated, so no need to worry on that front
** Or can the difference for nitrogen : (MD giving rms = 750m/s and kinetic theory: 550m/s) be justified saying kinetic theory assumes single hard-sphere models and also no attraction between particles. Whereas in MD, N2 is definitely not one sphere and LJ potentials have attraction and repulsion sitting inside of them.
Will be looking forward to your reply. Have a nice day. Do let me know if you need any more information from my end.
log.lammps.20200222_010920 (9.53 KB)
in-script (1.63 KB)