Foundations

This collection isolates ideas that recur across quantum chemistry and condensed-matter physics. Each note establishes notation, derives a working formula, and explains how the object appears in actual calculations.

Interaction

Two-electron Coulomb integrals

Chemists' and physicists' notation, permutational symmetry, scaling, and density fitting.

Read the note → Excitation

Quasiparticles

Dyson poles, renormalization factors, spectral widths, and the limits of the quasiparticle picture.

Read the note →

Tensor Methods