Multicolor groups for molecules and solids

Abstract The local magnetic moments of atoms in a molecule or solid can be designated by different colors. Magnetic groups, or 2-color groups, or black-and-white groups have been applied in crystallography to classify different magnets. Despite its successes in the past decades, the recent advent of altermagnets and p-wave magnets raises new challenges to this long-standing framework, which calls for a new and unified one. Here we develop a multicolor group classification framework to classify nonmagnetic materials and magnets with collinear or non-collinear magnetism, and with or without spin-orbit coupling (SOC), including the recently identified altermagnets and p-wave magnets. Especially, altermagnetic topological matter with SOC and p-wave magnets can also be diagnosed with multicolor groups, a task which cannot be accomplished by magnetic space groups and spin space groups. Moreover, insufficiencies and misconceptions of conventional magnetic group classification can be supplemented through this new framework. Multicolor group will serve as a new stage in the symmetry classification of matter.