Machine-learning effective many-body potentials for anisotropic particles using orientation-dependent symmetry functions

TL;DR

This paper develops orientation-dependent symmetry functions to improve machine learning potentials for anisotropic particles, enabling accurate simulations of complex colloidal systems with non-spherical shapes.

Contribution

Introduction of two- and three-body orientation-dependent descriptors for anisotropic particles, enhancing ML potential accuracy for non-spherical colloids.

Findings

Effective ML potentials accurately reproduce phase behavior of anisotropic colloids.

Orientation-dependent descriptors outperform spherical ones for non-spherical particles.

Validated potentials enable efficient simulations of complex colloidal systems.

Abstract

Spherically-symmetric atom-centered descriptors of atomic environments have been widely used for constructing potential or free energy surfaces of atomistic and colloidal systems and to characterize local structures using machine learning techniques. However, when particle shapes are non-spherical, as in the case of rods and ellipsoids, standard spherically-symmetric structure functions alone produce imprecise descriptions of local environments. In order to account for the effects of orientation, we introduce two- and three-body orientation-dependent particle-centered descriptors for systems composed of rod-like particles. To demonstrate the suitability of the proposed functions, we use an efficient feature selection scheme and simple linear regression to construct coarse-grained many-body interaction potentials for computationally-efficient simulations of model systems consisting of colloidal particles with anisotropic shape: mixtures of colloidal rods and nonadsorbing polymer, hard rods enclosed by an elastic microgel shell, and ligand-stabilized nanorods. We validate the machine-learning (ML) effective many-body potentials based on orientation-dependent symmetry functions by using them in direct coexistence simulations to map out the phase behavior of colloidal rods and non-adsorbing polymer. We find good agreement with results obtained from simulations of the true binary mixture, demonstrating that the effective interactions are well-described by the orientation-dependent ML potentials.