Hi @MZhong,
There are quite a few different issues to address here.
As background, we have had some recent unexpected experiences with ChatGPT, and in general the use of GenAI is still quite polarising in the academic community. I’m sorry that you experienced a bit of that backlash.
As far as I can see, in isolation, it is a reasonable experiment to use nph
integration together with Langevin thermostats to avoid thermostatting the system twice. I can’t tell you whether the final result will be “correct” or “wrong” (more on that later).
I can still tell you that there’s a general problem with your “multiple Langevin” idea, in the details section below.
Re: Langevin thermostats
The Langevin thermostat is completely local – it acts on every single particle in the system purely based on the particle’s own velocity.
In your original citation, the authors used velocity rescaling thermostats which are “global” – they adjust particle velocities based on the total kinetic energy of the system. In any nonequilibrium situation a global thermostat would allow larger inhomogeneities in temperature, while limiting only the total KE. That’s why the authors, in order to have more aggressive and localised thermostatting, needed to define multiple regional velocity rescaling thermostats.
Such an approach should not be necessary for Langevin thermostatting. Particles should behave very similarly under a single “global” Langevin thermostat as compared to multiple “local” Langevin thermostats.
But my detailed talk highlights two issues with your request – not that it’s a bad question, more that (as you’ve suggested) the LAMMPS forum isn’t necessarily the best place to ask.
Firstly, the issue you are grappling with is primarily scientific. It is true that (1) LAMMPS has very many features (2) the manual is very long to read through and quite dense at points. However, the central issue – that you are not sure how to thermostat your system – is separate. The LAMMPS manual is meant to tell you what each thermostat does; it cannot tell you which thermostat is right for your system. You need to know what you want to accomplish to answer that question for yourself.
Secondly, the LAMMPS forum is primarily run by volunteers and we mostly have experience with developing and maintaining the LAMMPS source code, alongside whatever projects we use the code for. Thus, if the LAMMPS code does something and you expected it to do something else, this forum is a good place to ask. If the LAMMPS code does something and you aren’t sure whether that is scientifically appropriate or not, we will not be well-placed to answer your question. I happen to have some unofficial experience with nonequilibrium thermostatting – but I am not experienced at all at solid state physics, solid state MD, or phase transitions, plus simply not having as many years’ experience as other volunteers here. And even if I did have that experience, it would not be a substitute for the eventual process of peer review during publication.
So – I can appreciate your frustration. But I am not sure you will get clear answers here. You may be better off contacting the authors of the paper you cited. You should also read MD textbooks, especially Frenkel and Smit (and Evans and Morriss on nonequilibrium topics).