I ran into some trouble with my latest simulations and since I’m quite new to the LAMMPS code, it would be great to get some help and maybe even a suggestions of improvement for my simulations.
Just to get a basic idea what the simulation aims for: My goal is to use the TraPPE UA force field of ethane (also the one of propane and the CO2 model) for adsorption processes on different metal surfaces. The simulations with CO2 worked in most cases very well, but ethane and propane caused almost always „nan“ errors.
That’s why I tried to just simulate the ethane and propane model without any other compounds at different densities (from densities in the gas phase to densities within the 2-phase region). The results of these tests showed that only simulations with low densities or low box dimensions worked. So, for example a simulation with a density of 60 kg/m^3 (gas phase, close to phase boundary) worked with a cubic box with an edge length of 50 Å but not with 120 Å. As a different example, a simulation with a density of 150 kg/m^3 (within 2-phase region) ran in a 20 Å box but not in a 50 Å box. I attached the input and a shortened data file of the latter one to this message.
A few more things, I’m a little wondering about, are:
- The Ewald summation is supposed to be used for the model, but I can’t make it work the way I tried to implement it so far
- I never got the minimize command to run, is it maybe connected to the rigid model I use? I thought it might speed up the equilibration of my simulations
- I wasn’t able to set the temperature damping parameter in all my simulations to lower values than 20 fs. Is it because of the neigh_modify command? I was actually used to work with temperature damping parameters of around 1-10 fs.
The version I use is the lmp_daily version from the 15th Nov 2018.
Here’s my input file: