Module two_electron 

Two-electron repulsion integrals (μν|λσ).

(μν|λσ) = ∫∫ χ_μ(r₁)χ_ν(r₁) (1/r₁₂) χ_λ(r₂)χ_σ(r₂) d³r₁ d³r₂

These are the most expensive integrals in quantum chemistry, scaling as O(N⁴) for N basis functions.

Algorithm

Uses the Obara-Saika scheme for electron repulsion integrals (ERIs).

Structs

TwoElectronIntegrals

Store two-electron integrals in a compact format.