[lammps-users] Lipid Bilayer Simulation using NVE ensemble.

Hello Everyone,

I am doing the Lipid Bilayer simulation using a mesoscopic model namely Dissipative Particle Dynamics. My goal is to study the Lipid bilayer thermal fluctuations, when the lipid bilayer is in tensionless state.
I was reviewing Literature on Simulations of Bilayer in tensionless state and how to set up the simulation parameters. In most of the literature which i came across, they use NPT or NVT ensembles. I manage to get lipid bilayer in tensionless state by changing lipid per area in the simulation box. My question is ,

  1. Is using the NVE ensemble the correct thing to do?.
  2. If I use the NVE ensemble, will my results have physical significance?

I read about different types of ensembles, but It was very hard for me to know which ensemble to use in my case.

Any help would be appreciated. Thanks.

Best Regards
Sheikh Salahudin
1st year PhD Student
INP Toulouse France

Two comments:

  • Like other beginners in using LAMMPS you seem to be confusing the “ensemble” your simulation is in with the “time integration fix” used in LAMMPS. Using “fix nve” or “fix nvt” or “fix npt” does *NOT automatically mean that your simulation is in NVE, or NVT, or NPT ensemble. Statistical mechanical ensembles have very specific definitions and while using any of those fixes can be a prerequisite to having a simulation in the corresponding ensemble, it is very often not the case for a variety of reasons. For example using fix langevin in addition to fix nve or fix press/berendsen or fix temp/rescale will change the ensemble and you will be in neither of those specific ensembles, at best you may be having an approximation of one of them.

  • What are suitable settings for your simulation (i.e. whether or not to use a thermostat, what kind of time integration, what potentials, and so on) are not so much a question for people with LAMMPS expertise but rather a topic to discuss with your adviser. This is about doing correct science and that is what your adviser is supposed to know the most about, since it is also his project that you are trying to realize.