wai-quantum 0.3.36: molecules and neural quantum states, held to exact answers #164

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dcharlot merged 3 commits from wai-quantum-nqs into main 2026-10-05 21:08:04 -04:00

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2026-10-05

Transaction Science

wai-quantum 0.3.36: molecules and neural quantum states, held to exact answers ...

quantum_chem: a molecule's ground state by DMRG from its FCIDUMP integrals.
- The second-quantised Hamiltonian lives on spin-orbital sites (alpha and
  beta side by side) via Jordan-Wigner, and compiles exactly into an MPO
  through OpSum. A sector penalty costs no bond, because its terms merge with
  the Coulomb ones.
- DMRG starts from Hartree-Fock with complete bases and keeps them complete
  (cutoff 0). With a positive cutoff it stalled at Hartree-Fock (Brillouin)
  or at the state's own rank.
- Full CI by direct CI over alpha/beta strings is the referee; it matches an
  independent program to 1e-9.
- Results: LiH and H2O reach full CI to 1e-13 in one sweep. N2 (20 spin
  orbitals) at bond 64 comes within 3.6e-4.

quantum_nqs: neural quantum states.
- Spin models on any graph, with exact diagonalisation and an OpSum form for
  DMRG.
- A real RBM with Marshall's sign; variational Monte Carlo by Metropolis
  chains or exact enumeration.
- Stochastic reconfiguration, solved in parameter or sample space, which
  give the same step.
- Results: 4x4 Heisenberg comes within 4.6e-4 of exact diagonalisation, and
  the critical 4x4 Ising model within its error bar. On 6x6 it meets DMRG
  at 3.6e-3, still descending.

DMRG's Lanczos now stops on the Ritz residual estimate, which re-pinned
DMRG. New pins chemistry_by_dmrg and neural_quantum_states pass natively and
under wasm32-wasip2. The CLI gains chem and nqs, byte-identical under WASI.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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2026-10-05 16:15:50 -04:00

Transaction Science

wai-quantum: exact MPOs from sums of operator strings ...

OpSum compiles a sum of products of one-site operators into an MPO by the
bipartite-graph construction: a minimum vertex cover per bond (Hopcroft-Karp
matching, König's theorem) sets the bond, and every coefficient is placed
once, so the MPO is exact. dmrg_mpo runs DMRG on any MPO from any start.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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2026-10-05 11:39:59 -04:00

Transaction Science

wai-quantum: MPOs with a tensor per site, held sparse ...

Each site carries its own operators between MPO bonds of their own size,
stored as its non-zero entries in the order the dense loops visited them, so
the uniform chains keep their bits (every pin unchanged).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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2026-10-05 11:35:54 -04:00