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[lammps-users] choosing the timestep in modeling membranes
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[lammps-users] choosing the timestep in modeling membranes

From: "jamal kazazi" <jamalkazazi@...1420...>
Date: Sat, 21 Oct 2017 03:10:39 +0200

Dear lammps users,
I'm trying to study buckling of thermally fluctuating membranes. The in-plane stiffness is achieved by bonding the points (atoms) and the bending is achieved by defining dihedrals. I have periodic boundary conditions as well.
I need to study the behavior for various values of bond stiffness (K). Consequently, I need to use a timestep that gives correct dynamics for different stiffness values. If I'm not mistaken, the correct way is to first calculate the smallest vibrational period of the system. So my first question is:
1- Is it possible in LAMMPS to calculate the vibrational frequencies (periods) to get the smallest period of my system and then calculate the timestep? (basically eigenvalue analysis).
As suggested in other posts, I have tried different timesteps for the same system (same velociy seed). I expected to see the same dynamics. Although the general behavior is the same for different timesteps, they are not exactly the same. So my second question is:
2- Do we expect to see exactly the same dynamics for systems that have been run with different timestep or a general agreement would suffice?
I'm attaching parts of the datafile, runfile and two graphs. The graphs are stress as a function of time for different timesteps. One graph is just the zoomed in version of the other.
I'd really appreciate your comments
J. Kazazi

Attachment: data.dat
Description: Binary data

Attachment: diff_dt_closer.jpg
Description: JPEG image

Attachment: diff_dt.jpg
Description: JPEG image

Attachment: runfile
Description: Binary data