Active matter with inertia

Dear LAMMPS users,

I already have used fix brownian/asphere + fix propel/self to run simulations for overdamped Lagevin equation with a Brownian active force (active brownian particles model). Now I would like to simulate active particles with inertia. The idea is have spheres with translational and rotational degrees of freedom governed by underdamp Langevin equation and a dipole (or quaternion) on this sphere to give it a propulsion force coupled or uncoupled to the sphere rotational dynamic (orientation of the sphere)

I think for coupling rotational dynamics I should use fix propel/self+fix langevin+fix nve/asphere, isn’ it? But then I have problems to uncoupled the dynamic for the particle and dipole (quaternion/orientation vector). Is there a way to do this in LAMMPS or should I perform my own code that only update the orientation of this dipole?


Unfortunately, I have very little specific advice to offer. The functionality you are using is rather new in LAMMMPS and a bit of a niche application within the existing LAMMPS user (and developer) community (otherwise it would have been implemented much sooner).

As with every research where you move beyond the boundaries of what is common knowledge and within your personal area of expertise, my advice is to construct careful test examples and verify on a step-by-step basis that every modification you do to your input and every feature you add will result in exactly the intended behavior. This is not always easy to do, when you are moving into new functionality of a software, since the documentation may be limited and the code not overly well tested. So it is likely that you will also need to study the relevant source code and confirm that it does what you expect it does. Ultimately, I suspect you may need to do your own C++ programming to get exactly what you want, or - perhaps - search for some other MD software that already has the feature(s) you are looking for.

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