Native Hartree-Fock (dense_evolution.native_hf)
A from-scratch, JAX-vectorized ab-initio Hartree-Fock engine — overlap,
kinetic, nuclear-attraction, and electron-repulsion integrals over s/p
Cartesian Gaussian shells via the Obara-Saika recursion (Obara & Saika,
J. Chem. Phys. 84, 3963, 1986), each shell-pair/quartet batched with
jax.lax.scan/jax.vmap and compiled with jax.jit instead of looping
in the Python interpreter.
It exists because PennyLane's own differentiable Hartree-Fock solver
(qml.qchem, method="dhf") builds these same integrals through a
Python-level loop wrapped in its autograd-tracing numpy layer — correct,
but profiled directly at 482 of 483 total seconds for Si2/STO-3G, almost
entirely per-scalar-op tracer overhead rather than real FLOPs. This
module only replaces the integral/SCF stage; the converged result still
goes to PennyLane's own fermionic_observable + jordan_wigner for the
qubit mapping, since that stage is already fast (under 2 seconds) and
well-tested. Basis-set parameters come from the
basis_set_exchange
package, so any element it has STO-3G data for is reachable, not just
PennyLane's bundled H–Ne table. An element needing d-orbitals or higher
(e.g. Fe) fails with a clear NotImplementedError naming the real
limitation, not a silent wrong energy for an incomplete basis.
Design and algorithm structure were informed by studying
lowdanie/hartree-fock-solver
("slaterform", Apache-2.0) as a reference for structuring the Obara-Saika
recursion with jax.lax.scan, and by PennyLane's own white paper
(Delgado et al., "Differentiable quantum computational chemistry with
PennyLane", arXiv:2111.09967) — no
source code from either project is copied here. Verified element-wise
against an independent JAX Hartree-Fock implementation (slaterform) to
machine precision on individual integrals and to 10 significant figures
on Si2/STO-3G's full SCF energy.
dashboard_core.hamiltonians calls this engine automatically —
bridge.build_qubit_hamiltonian — whenever a requested molecule uses an
element outside PennyLane's own STO-3G table; existing molecules
(H2/HeH+/H3+/LiH/H2O) are unaffected and keep using PennyLane's dhf
pipeline directly. See Dashboard Core — Hamiltonians
for the dispatch logic and the Si2 catalog entry this engine backs.
::: dense_evolution.native_hf.bridge
::: dense_evolution.native_hf.scf
::: dense_evolution.native_hf.basis
See also: Dashboard Core — Hamiltonians
for the production entry point (MOLECULE_CATALOG's Si2 entry), and
dashboard_core.vqe for the ansatz circuits
optimized against Hamiltonians this engine can build.