A general model for frictional contacts in colloidal systems

[khofmann6]

Description

I added a new class of pair force (similar to aniso). Here the relative "surface" velocity of two interacting particles is calculated (only for spherical particles) and is used to calculated a frictional force which may depend on this relative velocity. I added three frictional contact models (constant. linear, and Coulomb-Newton).

For more details see the preprint: https://arxiv.org/abs/2507.16388

Motivation and context

Frictional contacts couple translational and rotational degrees of freedom, which may affect the collective behavior of, e.g., colloids under shear and chiral active matter. Deterministic frictional contact models on the colloidal scale are thermodynamically inconsistent. This proposed model, which is roughly equivalent to DPD for anisotropic potentials, solves this inconsistency with a additional pairwise stochastic term.

How has this been tested?

The code was used to create the data presented in: https://arxiv.org/abs/2507.16388

pytest are still missing
Detailed documentation is missing

Checklist:

• I have reviewed the Contributor Guidelines.
• I agree with the terms of the HOOMD-blue Contributor Agreement.
• My name is on the list of contributors (sphinx-doc/credits.rst) in the pull request source branch.
• I have summarized these changes in CHANGELOG.rst following the established format.

[joaander]

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