Approximation schemes built from symmetric polynomials, using spherical harmonics to enforce rotation invariance.
The main scheme currently implemented is based on the Atomic Cluster Expansion (ACE) described in
Drautz, R.: Atomic cluster expansion for accurate and transferable interatomic potentials. Phys. Rev. B Condens. Matter. 99, 014104 (2019). doi:10.1103/PhysRevB.99.014104
note: this repository builds SHIPs.jl
but incorporates multiple extensions, which will be documented in due course.