Hi, I'm working on a project using LAMMPS. I am very new to the software and find the documentation doesn't always answer the fundamental questions I have. I noted previous LAMMPS queries were posted on this forum, although I am from a mechanical/materials engineering background. I am trying to build a substrate with three regions: one under NVE dynamics, an additional region acting as a thermostatic boundary (NVT dynamics) and a final fixed region (effectively the same idea as Goel et al. and Wang et al.). My simulation is working well when the substrate is one region, all NVE; however, I am running into errors---possibly due to a misunderstanding of the syntax---when I try to add in these boundaries. Any help on how to define these regions would be greatly appreciated.