Periodic-method requirements from `basissetdev`¶

Audience: the periodic-methods main development chat. Authors: basissetdev, M. F. Peintinger. Date: 2026-05-08; last refresh 2026-05-13. Status: living document; rebased onto main as features land.

2026-05-13 refresh. Since the initial audit on 2c7c7df, Codex landed the native GDF backend (periodic_rhf_gdf.py, periodic_k_gdf.py, periodic_gdf_blocks.py), replacing the retired in-process PySCF periodic backend, which CLAUDE.md § 10 now formally forbids. CRYSTAL-style FMIXING (previous-Fock mixing) and Fermi-Dirac smearing are wired through the GDF and Ewald multi-k paths. Shared SCF mixing helpers (validate_fraction_01, mix_fock_matrices) live in cpp/include/vibeqc/scf_mixing.hpp, new basissetdev work must reuse these, never duplicate (manifest rule). See per-requirement status notes below.

This is the punch list of periodic capabilities basissetdev needs in order to reproduce the published pob-paper test sets in vibe-qc. The papers in scope are:

M. F. Peintinger, D. Vilela Oliveira, T. Bredow, J. Comput. Chem. 34, 451 (2013). [pob-TZVP, PT2013]
D. Vilela Oliveira, J. Laun, M. F. Peintinger, T. Bredow, J. Comput. Chem. 40, 2364 (2019). [pob-TZVP-rev2 + pob-DZVP-rev2, VO2019]

Together they enumerate roughly 70 binary and ternary ionic / semiconducting / TM-oxide / metallic systems plus a 9-compound subset of the X23 molecular crystals. Each requirement here is tagged with the table(s) it gates and the count of compounds that become runnable when it lands.

Conventions¶

P0: hard blocker for ≥10 compounds in the test set.
P1: blocker for 1-10 compounds, or for cross-method validation.
P2: nice-to-have / faithful reproduction of CRYSTAL workflow.
vibe-qc state originally audited on commit 2c7c7df of basissetdev; refreshed 2026-05-13 on commit 1bf32cc.
Feature counts below are conservative, orthorhombic is the most permissive cell shape vibe-qc currently handles.

Test-set overview¶

Source	Table	Cell shape	Compounds	Listed
PT2013	T4	cubic	12	LiCl, NaCl, LiF, NaF, KF, CaF₂, K₂O, MgO, CaO, LiH, NaH, KH
PT2013	T5	hexagonal	10	BeF₂, ScCl₃, MgBr₂, BeO, α-SiO₂, B₂O₃, Al₂O₃, NaNO₃, MgCO₃, FePO₄
PT2013	T6	orthorhombic	5	BeBr₂, NaNO₂, CaH₂, CrCl₂, GeSe
PT2013	T8	cubic semiconductor	22	C(diamond), Si, Ge, AlP, AlN, Na₂Se, GaAs, GaP, ZnS, MnSe, ZnSe, β-BN, β-SiC, TiC, Cu₃N, VC, VN, TiN, CrN, K₂S, MnS
PT2013	T9	hexagonal semicond.	9	NiAs, α-SiC, α-BN, B₄C, ScB₂, CoS, CuS, GaF₃, GeO₂
PT2013	T10	cubic TM oxide	7	Sc₂O₃, MnO, FeO, CoO, NiO, Cu₂O, ZnCr₂O₄
PT2013	T11	hexagonal/tetragonal TM oxide	4	V₂O₃, Cr₂O₃, ZnO, TiO₂(rutile)
PT2013	T12	cubic metal	11	Li, Na, K, Ca, Sc, V, Cr, Fe, Ni, Cu, Al, Ni₃Al
PT2013	T14	HF cubic ionic	12 (subset of T4 + K₂S)	LiCl, NaCl, LiF, NaF, KF, CaF₂, K₂O, MgO, CaO, LiH, NaH, KH
VO2019	T2	cubic ionic	14	+ KBr, SiF₄
VO2019	T3	hexagonal ionic	10	(overlap with PT2013 T5)
VO2019	T4	orthorhombic ionic	4	NaNO₂, CaH₂, CrCl₂, GeSe
VO2019	T6	cubic semicond.	14	(subset of PT2013 T8)
VO2019	T7	hex semicond.	9	(subset of PT2013 T9)
VO2019	T9	cubic TM oxide	7	(overlap with PT2013 T10)
VO2019	T10	hex/tet TM oxide	5	+ TiO₂(anatase)
VO2019	T14	molecular crystal	9	from X23, dispersion-dominated
VO2019	Figs 2-7	molecular hydride dimer	~30	H_n A-AH_n at 1.4-5 Å, A=Li-Br

Total unique compounds: ≈75. Counted by cell shape: roughly 40 cubic, 20 hexagonal, 10 orthorhombic/tetragonal, plus the molecular-crystal subset.

Hard requirements¶

R1, Non-orthorhombic Ewald [P0]¶

The current ewald_j / periodic_*_ewald family rejects any cell that is not strictly orthorhombic, because the FFT Poisson solver indexes the real-space grid by Cartesian (a×b×c) box dimensions. Hexagonal, trigonal, and tetragonal cells with non-orthogonal a/b or a/c are refused at SCF entry with:

“system lattice must be orthorhombic (FFT Poisson solver does not yet support triclinic cells).”

The test-set fraction that requires non-orthorhombic Ewald:

Hexagonal: PT2013 T5 (10), PT2013 T9 (9), PT2013 T11 (3), VO2019 T3 (10), VO2019 T7 (9), VO2019 T10 (4), ≈32 unique compounds blocked.
Tetragonal: TiO₂(rutile), TiO₂(anatase), 2 compounds.

Acceptance: run_rhf_periodic_multi_k_ewald3d accepts hexagonal (a, b=a, c, α=β=90°, γ=120°) cells; total energy on α-Al₂O₃ (R-3c) at experimental geometry agrees with PySCF.pbc.GDF to 100 µHa per formula unit. Tetragonal (P4/mmm and P4₂/mnm spacegroups) covered by the same fix.

Note for kpoints.py: the hexagonal/trigonal Γ-centring guard is already in place; the work is on the Poisson side. No changes to the k-mesh API required.

R2, Multi-k MP-grid SCF on production basis sizes [P0]¶

Status as of 2026-05-13: partially landed.

Native GDF backend live: periodic_rhf_gdf.py (Γ-only), periodic_k_gdf.py (multi-k), periodic_gdf_blocks.py (Bloch assembly from lattice blocks). The in-process PySCF periodic backend was retired (commits 545db04 / 7ab9384), manifest § 10 now forbids importing PySCF inside vibe-qc; parity testing against PySCF happens out-of-process via examples/regression/ runner_pyscf.py. The CaF₂ pob-TZVP RKS-PBE CRYSTAL14 regression fixture (e46211c) is the first cubic-ionic parity test exercising basissetdev’s .d12 sidecar pipeline (Phase 14h).

Already landed in the multi-k path:

smearing_temperature Fermi-Dirac occupations (periodic_rhf_multi_k_ewald.py lines 33-34, 156, 445; periodic_k_gdf.py line 76). Unit-bearing strings (“0.01 Ha”, “300 K”) accepted via the GDF gamma path (7eacfd3). Free energy with E - T·S correction surfaced in the result bundle (periodic_rhf_gdf.py line 548).
fock_mixing (CRYSTAL FMIXING-equivalent) wired through both Γ-GDF and multi-k. Validation against MgO PBE/POB-TZVP CRYSTAL14 totals via examples/regression (commit 7c02666).
Low-dimensional MP meshes (1D / 2D systems) accepted by the legacy path (f4d95f9).
Periodic dimensionality is logged in GDF jobs (56fd2e7).

Still open:

Validation against CRYSTAL k-mesh density at production sizes. PT2013 / VO2019 use Pack-Monkhorst grids around 8×8×8 for rocksalt ionics, 4×4×4 for the larger sesquioxides. vibe-qc tests have so far focused on small (2×2×2 to 4×4×4) grids; the linear-system size at full pob-TZVP × 8×8×8 is unmeasured. The Phase-14h .d12 sidecars now make this measurable: same compound, same basis, same k-mesh, on both codes via vq. Bench needed.
Smoke test on metallic Cu (FCC, T12). Smearing is in; the metal-specific SCF flow at production size hasn’t been benchmarked. T12 metals (Li, Na, K, Ca, Sc, V, Cr, Fe, Ni, Cu, Al, Ni₃Al) inherit any remaining issues.

Acceptance: MgO total energy at Γ + 8×8×8 Pack-Monkhorst with pob-TZVP/PW1PW agrees with PT2013 SI Table 1 (E = −275.477 595 Ha per cell) to 1 mHa. Metallic Cu (FCC) converges with smearing σ = 0.01 Ha and reproduces the 2013 Table 12 lattice constant (3.506 Å) to 0.01 Å.

Reuse, don’t duplicate. Shared mixing helpers (validate_fraction_01, mix_fock_matrices) in cpp/include/vibeqc/scf_mixing.hpp are the canonical implementation across molecular + periodic, per manifest § 10. Any new basissetdev SCF-control work plugs into this header.

R3, Stable open-shell UKS / UHF for transition-metal oxides [P0]¶

Status as of 2026-05-13: still blocked. No change since the 2026-05-08 audit; the broken-symmetry initial guess for AFM ground states has not landed. Basissetdev’s Goal 3 ships the 6 AFM-II compounds (MnO, FeO, CoO, NiO, α-MnS, α-MnSe) as BLOCKED ON: R3 stubs, their .py inputs are wired so the moment R3 lands, only the initial-guess hook needs filling in. The .d12 sidecars (Phase 14h) skip emission for AFM compounds since the CRYSTAL ATOMSPIN block requires the same magnetic- ordering decision; both emit when R3 + ATOMSPIN-aware generator support land together.

The multi-k UKS (periodic_uks_multi_k_ewald.py) and UHF (periodic_uhf_multi_k_ewald.py) modules exist. The blocker is not the kernel but the initial-guess strategy for antiferromagnetic ordering. Currently both default to Hcore → identical α/β densities → SCF converges to the closed-shell solution by symmetry. This is the wrong basin for AFM systems.

Compounds blocked (counted once across PT2013 + VO2019): MnO, FeO, CoO, NiO (T10/T9), Cr₂O₃, V₂O₃ (T11/T10), CrCl₂ (T6/T4), CrN, MnS, MnSe (T8/T6), 10 transition-metal compounds.

Acceptance: broken-symmetry initial guess (Mulliken-localised single-atom UKS densities tiled into the AFM unit cell, optionally with a small spin-symmetry-breaking field on the magnetic sublattice). NiO total energy with pob-TZVP/PW1PW reproduces PT2013 SI Table 1 (−3167.495 768 Ha per cell, two formula units in the AFM-II unit cell) to 1 mHa.

R4, PW1PW hybrid functional [P0]¶

PW1PW is the workhorse functional for PT2013 and VO2019. It is the 1-parameter global hybrid of Bredow & Gerson (T. Bredow, A. R. Gerson, Phys. Rev. B 61, 5194 (2000), DOI 10.1103/PhysRevB.61.5194), originally introduced as the “HF+PWGGA hybrid approach” in §III.D of that paper. The mixing α = 0.20 was empirically optimised on MgO / NiO / CoO bulk properties and coincidentally matched the B3LYP exchange-mixing fraction. The “PW1PW” name came into use in subsequent CRYSTAL-community papers (Peintinger 2013 onward).

Definition:

E_x = 0.20 · E_x^HF + 0.80 · E_x^PW91
E_c = E_c^PW91

Where PW91 = Perdew-Wang 91 GGA (libxc IDs XC_GGA_X_PW91 = 109 and XC_GGA_C_PW91 = 134). The hf_exchange_fraction mechanism in periodic_rks_multi_k_ewald.py already supports α = 0.20 mixing; what’s missing is the named entry in vibe-qc’s functional registry that resolves "PW1PW" to this triplet. Status 2026-05-13: still missing, no registry alias landed since the audit. The 33 .d12 parity sidecars in Phase 14h currently emit the no-DFT (HF) form; once PW1PW resolves, the generator just flips method="pw1pw" and CRYSTAL’s PW1PW keyword does the matching parity run.

Note: PW1PW is distinct from PBE0 (PBE-based hybrid, α = 0.25), B3LYP (three-parameter Becke88 + LYP + VWN5), and plain PW91 (no HF mixing). Do not silently substitute any of these for PW1PW in benchmarks against the pob SI tables.

Acceptance: functional="PW1PW" resolves to the Bredow-Gerson hybrid with α = 0.20 and PWGGA (X + C) DFT components. RKS total energy on MgO with pob-TZVP at converged k-mesh equals PT2013 SI Table 1 (E = −275.477 595 Ha per cell) to 1 mHa. (Without R1+R2 this is testable only for cubic ionics and TM oxides.)

The Bredow-Gerson 2000 paper additionally benchmarks HF+LYP, HF alone, B3LYP, BLYP, PBE, and plain PWGGA on MgO / NiO / CoO. If the periodic chat wants a smaller cross-validation acceptance target, the seven-functional comparison from that paper’s Tables I-IV is a clean test fixture: ≈30 (compound × functional) data points at known geometry. PDF reference: /private/tmp/bredow2000.pdf on the user’s machine; user-shipped 2026-05-08.

R5, Geometry optimisation in periodic [P0]¶

Status as of 2026-05-13: still blocked. Gradients are present and have been extended (RKS gradients, periodic_gradient_rks.py; open-shell gradients, periodic_gradient_open_shell.py; multi-k gradients, periodic_gradient_multi_k.py), but no atom-or-lattice relaxation driver. Phase 14h .d12 sidecars fix the lattice at the experimental value so the parity test isn’t also gated on this requirement.

The molecular path has _optimize_geometry (runner.py); the periodic path has gradients (periodic_gradient*.py) but no relaxation driver. Every line of every pob-paper table is a relaxed geometry: lattice parameters and atomic positions are optimised against the basis. Without relaxation, comparison to the paper tables is impossible.

Two flavours needed:

Atomic-position-only relax at fixed lattice. Required for T5/T6/T9/T10/T11/T8 (anything with internal coordinates), ≈40 compounds.
Lattice + atomic-position simultaneous relax. Required for every cell in the test set, ≈75 compounds.

Acceptance: wrap the existing periodic-gradient drivers behind an ASE BFGS / FIRE optimiser that updates both atomic positions and the lattice tensor. NaCl (Fm-3m) with pob-TZVP/PW1PW relaxes from 5.5 Å starting cell to 5.609 ± 0.005 Å (PT2013 Table 4), atomic positions stay at (0, 0, 0) and (½, ½, ½) by symmetry.

For the lattice-tensor side, the stress tensor is the natural primitive but is currently not in vibe-qc (memory: deferred to v0.8). A first cut can use finite-difference lattice gradient (perturb each lattice parameter by ε, recompute total energy, divide) and feed that to the BFGS optimiser. Slower than analytical stress but unblocks the test set.

R6, Counterpoise / BSSE for periodic crystals [P1]¶

VO2019’s central novelty is the BSSE-aware re-optimisation. They use CRYSTAL’s ATOMBSSE to compute the per-atom counterpoise correction in a periodic crystal (ghost-atom basis on the heavy atom, no nuclei, no electrons, in the otherwise-real lattice).

vibe-qc has no equivalent yet. To reproduce VO2019 numbers, needed; to use the rev2 basis sets, not strictly needed (the basis already incorporates the BSSE-aware exponent shift).

For Goal 4 of basissetdev (re-running the rev2 optimisation in vibe-qc), counterpoise IS required as part of the objective function. Hence P1 not P0.

Acceptance: ghost_atoms=[(symbol, position), …] parameter on PeriodicSystem that places basis functions but no nuclei / no electrons. NaH ATOMBSSE matches CRYSTAL within 1 mHa.

Cross-method validations¶

R7, Functional zoo: PBE, PBE0, B3LYP, BLYP, HSE [P1]¶

PT2013 and VO2019 cite cross-validation against B3LYP and PBE0 in side notes. vibe-qc’s libxc-based functional registry should already accept these strings (the runner advertises them). What’s missing is end-to-end verification at converged k-mesh + multi-k SCF for the cubic ionic subset (which is the easy 12-compound benchmark). Listing here so the periodic chat doesn’t deprioritise.

Acceptance: the 12 cubic ionics from PT2013 T4 run with PBE, PBE0, B3LYP, BLYP, HSE06 (each), in addition to PW1PW.

R8, Wu-Cohen GGA (WC) [P2]¶

WC (XC_GGA_X_WC = 118; correlation typically PBE) is used in PT2013 for the metallic systems (preliminary basis-set optimisation). Easy to add, libxc has it; the question is the registry alias.

Acceptance: functional="WC" resolves to WC-X + PBE-C.

Numerics & screening¶

R9, TOLINTEG-equivalent screening control [P1]¶

linear_dependence.py and eigs_preflight.py already point at LatticeSumOptions.schwarz_threshold as the TOLINTEG-equivalent knob. PT2013 explicitly mentions ITOL5 = 27 (vs default 14) for ionic SCF convergence, i.e. extremely tight Coulomb-tail screening. Need to verify schwarz_threshold covers ITOL4 (Schwarz two-electron) AND ITOL5 (penetration / overlap-based truncation distance). If they’re conflated in vibe-qc, surface separately.

Acceptance: running the sulfide subset (ZnS, MnS, K₂S, CoS, CuS) with default screening converges; bumping the equivalent of ITOL5 to 27 closes any residual SCF oscillation.

R10, Atomic-reference HF energies for cohesive / atomization [P1]¶

PT2013 Table 13 reports atomization enthalpies. To compute these you need (a) the periodic total energy and (b) the isolated-atom total energy in the same basis. The molecular path handles (b) at the symmetry-broken UHF level; the question is exposing a single-atom reference path that accepts a Mulliken-style fractional- occupation specification (atoms in PT2013 are computed with “neutral atomic configurations from our website”, the .single files in the Bredow archive).

Acceptance: vq.atomic_reference_energy(symbol, basis, configuration="neutral") returns the SCF energy for the open-shell atom with the published occupation, for every element in pob-TZVP.

Lower-priority polish¶

R11, D3(BJ) for periodic [P2]¶

dispersion.py exists in molecular path. VO2019 Table 14 applies D3(BJ) on top of pob-TZVP / pob-TZVP-rev2 for the X23-subset molecular crystals; the deltas drive ≈2-3 % lattice-constant improvements. Periodic D3 is an additive post-SCF step on the relaxed geometry, needs lattice summation of the C₆/C₈ pairs but no SCF intrusion.

Acceptance: ZnO + D3(BJ) with pob-TZVP-rev2 reproduces VO2019 Table 14 D3-corrected c to 0.01 Å.

R12, `ATOMBSSE` for the molecular hydride dimers [P2]¶

The 2019 BSSE-correction recipe uses molecular counterpoise on H_n A-AH_n dimers (computed in ORCA 3.0 with MP2). vibe-qc’s molecular DF MP2 was wired in v0.7.3. A native vibe-qc version of this step is needed for Goal 4 (re-running the rev2 optimisation without external ORCA dependencies).

Acceptance: counterpoise(H₂O)₂ at 2.5 Å with vibe-qc/MP2 matches ORCA 3.0 MP2 to 1 mHa.

Basis-optimization gradient infrastructure¶

R13, Lattice-summed exponent/coefficient-derivative 3c/2c kernel [P1]¶

Status as of 2026-06-21: ask raised; not started. New requirement from the periodic basis-optimization gradient effort (the crystal OPTBASIS analogue; see PERIODIC_GRADIENT_DESIGN.md).

The periodic basis-parameter gradient assembles, per k-point,

dE/d(eta) = Sum_k w_k Re[ tr(P dHcore/d(eta)) + 1/2 tr(P dG/d(eta))
                          - tr(W dS/d(eta)) ].

The clean one-electron pieces dS(k)/d(eta) and dT(k)/d(eta) are done (Phase P1) in Python, by Bloch-summing the molecular overlap_/kinetic_exponent_ derivative bindings between a home-cell shell and its image. The hard remaining piece (Phase P2) is the two-electron Coulomb derivative dG(k)/d(eta) and the nuclear derivative dV(k)/d(eta). Both are built from the lattice-summed GDF/Ewald 3-index (P|mu nu) and 2-index (P|Q) integrals with the Ewald-3D gauge, so their basis-parameter derivative needs the d/d(eta) sibling of the existing d/dR gradient kernels compute_3c_eri_lattice_gradient_weighted / compute_2c_eri_lattice_gradient_weighted (used today by periodic_gdf_gradient.py for nuclear gradients).

This is the one piece of the periodic basis-gradient that lives in the periodic-SCF integral layer (cpp/), which basissetdev does not own, hence this ask (CLAUDE.md s11). It is not a hard blocker: a first working basis-gradient can use an integral-FD dG(k)/dV(k) behind the assembly’s provider with no C++ change. R13 enables the fully analytic, production route. Marked P1 (blocks cross-method validation of the periodic optimizer), not P0.

Acceptance: a binding analogous to compute_3c_eri_lattice_gradient_weighted that, given a target shell and a primitive index (plus a coefficient variant), returns the weighted contraction of the lattice-summed 3c/2c integral derivative w.r.t. that primitive’s exponent (or coefficient). Validated to 1e-6 or better vs a central integral FD of the Bloch-summed 3c/2c tensor at fixed k, on a small cell. Until it lands, basissetdev proceeds with the integral-FD fallback behind the provider.

Out of scope here (other chats / future versions)¶

Periodic stress tensor. Memory: reserved for vibe-qc v0.8. Once landed, R5 lattice opt becomes analytical instead of FD.
Slab / surface support. Same: v0.8 deliverable.
AutoAux periodic aux basis. Owned by the DF dev chat (memory: feedback_aux_basis_routing.md).
CCM / cyclic-cluster method. Memory: deferred to a later vibe-qc version.

Suggested implementation order¶

The order that unblocks the most of the test set per landed feature:

R5 atomic-position relax + R4 PW1PW + R7 functional verification → unlocks 12 cubic ionics from PT2013 T4 + 12 cubic ionics from VO2019 T2 (overlap) + 22 cubic semiconductors from PT2013 T8 + 7 cubic TM oxides from PT2013 T10 = ≈40 compounds runnable.
R3 broken-symmetry UKS guess → unlocks the 10 TM oxide / chloride / nitride compounds.
R1 non-orthorhombic Ewald → unlocks the 32 hexagonal/ tetragonal compounds. Big single-feature payoff.
R5b lattice relax (FD lattice gradient) → enables the actual lattice-constant comparison vs. paper tables for everything above.
R2 metallic k-mesh smearing → unlocks the 12 cubic metals.
R6 ATOMBSSE periodic + R12 molecular counterpoise → unlocks the rev2 re-optimisation pipeline for Goal 4.

Status table (as of refresh on `1bf32cc`, 2026-05-13)¶

Req	Title	State
R1	Non-orthorhombic Ewald	MISSING
R2	Multi-k MP-grid SCF	partial, native GDF + smearing + FMIXING landed; production-size CRYSTAL14 parity bench outstanding
R3	Open-shell UKS for AFM TM oxides	partial, kernels exist, BS guess still missing
R4	PW1PW hybrid functional	partial, `hf_exchange_fraction` exists, registry alias still missing
R5	Periodic geometry / lattice optimisation	MISSING, gradients exist (RKS / open-shell / multi-k), no relax driver
R6	Counterpoise / BSSE periodic	MISSING
R7	PBE/PBE0/B3LYP/BLYP/HSE verification	partial, registry exists, end-to-end untested at production size
R8	WC GGA functional	partial, libxc has it, registry alias TBD
R9	TOLINTEG-equivalent screening control	partial, `schwarz_threshold` exists, ITOL4/5 conflation TBD
R10	Atomic-reference HF for atomisation	partial, molecular UHF works, fractional-occ wrapper missing
R11	D3(BJ) for periodic	partial, molecular path exists, periodic glue missing
R12	ATOMBSSE molecular dimer	partial, molecular MP2 works, counterpoise glue missing
R13	Lattice-summed exponent/coeff-deriv 3c/2c kernel	NOT STARTED, ask raised 2026-06-21; integral-FD-behind-provider fallback unblocks P2 meanwhile

Shared infrastructure now in `main` (basissetdev reuses, never duplicates)¶

Header / module	Provides	Notes
`cpp/include/vibeqc/scf_mixing.hpp`	`validate_fraction_01`, `mix_fock_matrices`	Canonical Fock-mixing primitives; molecular UHF/UKS + periodic GDF/Ewald all dispatch here.
`python/vibeqc/periodic_rhf_gdf.py`	Γ-only RHF GDF backend	Native; no PySCF runtime dependency.
`python/vibeqc/periodic_k_gdf.py`	Multi-k GDF	Cubic / orthorhombic / low-dim lattice families covered.
`python/vibeqc/periodic_gdf_blocks.py`	Bloch assembly from lattice blocks	Underpins both Γ and multi-k.
`examples/regression/runner_pyscf.py`	Out-of-process PySCF parity	Manifest § 10: PySCF is external; vibe-qc never imports it.
`examples/basisset_dev/inputs/*.d12` (Phase 14h)	CRYSTAL14 parity sidecars	33 cubic ionic / semiconductor / TM-compound `.d12` decks; runs out-of-process via `vq submit` + `run-crystal.sh` (memory: `reference_crystal14_via_vq.md`).

Hand-off note¶

This document is the deliverable from basissetdev to the periodic-methods chat. It does not prescribe how each requirement is implemented; that is the periodic chat’s call. When a requirement lands, mark it ✅ here and update PLAN.md Goal 2 status. basissetdev rebases onto main after each landing.

Periodic-method requirements from basissetdev¶