integral-core

Layer-1/2 integral engines and operator layer for integral, a native-Rust library for Gaussian integrals in quantum mechanics.

This crate hosts:

• One-electron Obara–Saika engine — overlap, kinetic, nuclear attraction, multipole.
• OS/HGP two-electron engine — flat-array HRR + m-marching VRR + reusable arena.
• Rys two-electron engine — small-footprint quadrature path for all angular momenta.
• Operator DSL — one-electron integrands as polynomials in r and p = −i∇.
• Geometric first derivatives — via the Gaussian center-derivative relation.

Most users want the higher-level integral driver crate rather than this one. #![forbid(unsafe_code)], pure stable Rust.

Licensed under Apache-2.0.