Feature matrix

The capability matrix for the v0.15.x release line (codename Neese’s Cheetah). For when each feature shipped, see CHANGELOG.md. For what’s coming next, see roadmap.md.

Molecular SCF

Method	Driver	Open-shell	Gradient	Hessian (FD)	Hessian (analytic)	MP2	Validated vs PySCF
RHF	run_rhf	-	✓	✓ (compute_hessian_fd)	✓ (compute_hessian_rhf_analytic)	✓ (run_mp2)	✓ machine precision
UHF	run_uhf	✓	✓	✓	(roadmap 17c)	✓ (run_ump2)	✓ machine precision
RKS	run_rks	-	✓	✓	(roadmap 17e)	-	✓ grid-accuracy
UKS	run_uks	✓	✓	✓	(roadmap 17f)	-	✓ grid-accuracy
ROHF	run_rohf	✓ (spin-pure)	✓ analytic	✓ (freqs)	(roadmap)	✓ (run_rohf_mp2, semicanonical)	PySCF-parity tests¹
ROKS	run_roks	✓ (spin-pure)	✓ (FD, opt)	(roadmap M5b)	(roadmap M5b)	-	PySCF-parity tests¹

¹ ROHF/ROKS: the Roothaan-coupling + energy math is verified directly (closed-shell→RHF/RKS reduction, SCF stationarity, and ROKS fractional degenerate frontier shells such as OH(2Pi)); the end-to-end PySCF-parity and ROHF-on-singlet==RHF tests are written and run in the full dev-box suite (tests/test_rohf.py, tests/test_roks.py).

Mean-field functionals libxc supports work through RKS / UKS / ROKS (500+ functionals including LDA, GGAs, hybrid GGAs, the τ-dependent meta-GGA family (TPSS, TPSSh, M06-L, M06-2X, SCAN, r²SCAN, r²SCAN01), and the range-separated hybrids ωB97X, ωB97X-D, and the VV10-paired ωB97X-V / ωB97M-V; direct double-hybrid ROKS calls still route through the double-hybrid dispatcher). HF and DFT analytic gradients are available for LDA, GGA, hybrid-GGA, and the τ-dependent meta-GGA family (modulo the f-shell gradient bug on open-shell UHF / UKS). Meta-GGA analytic Hessians and range-separated-hybrid analytic gradients are still queued. Range-separated hybrids run via direct SCF (not yet density-fitting).

Wavefunction methods (v0.9.0-v0.12.0)

Non-mean-field electronic-structure methods that do not conceptually rely on a Hartree-Fock reference. All reachable through run_job(method=…) and as a standalone vibeqc.solvers import. See user_guide/non_hf_solvers.md and the non_hf_solvers tutorial.

Post-HF correlation methods

Correlated wavefunction methods that build on a Hartree-Fock reference. All reachable through run_job(method=…).

Method	run_job(method=…)	Reference	Notes
CISD	"cisd" or method="ci", citype="cisd"	HF orbitals	Fixed-space variational singles+doubles CI via vibeqc.cisd; CISDOptions controls roots and determinant-space guards.
CC2	"cc2" or method="ci", citype="cc2"	RHF	Ground-state second-order approximate coupled cluster. The singles projection is complete and the doubles equation retains the T1-transformed Hamiltonian plus [F,T2]; DF and exact-integral routes are supported. Closed-shell energies only; no perturbative triples. Validated against a spin-orbital oracle and ORCA AUTOCI-CC2.
CCSD	"ccsd"	RHF / UHF / ROHF	Canonical dense CCSD, density-fitted by default or on exact four-index integrals (CCSDOptions(density_fit=False), conventional cross-code parity route); closed-shell and open-shell (UCCSD on a UHF reference, ROHF-reference via the spin-orbital kernel), auto-dispatched from the SCF reference. Also run_ccsd with CCSDOptions.
CC3	"cc3" or method="ci", citype="cc3"	RHF	Ground-state iterative CC3 with converged singles/doubles and approximate connected triples regenerated at every iteration. Exact MO integrals and frozen cores are supported. Energy-only and benchmark-scale because the dense determinant representation grows combinatorially. Validated against out-of-process ORCA 6.1 UHF AUTOCI-CC3 on closed-shell references.
CCSDT	"ccsdt" or method="ci", citype="ccsdt"	RHF / ROHF	Full iterative singles, doubles, and triples from the exact determinant-space similarity projection. Exact MO integrals, frozen cores, and common-orbital open shells are supported. Energy-only and benchmark-scale because the dense determinant representation grows combinatorially.
CCSD(T)	"ccsd(t)"	RHF / UHF / ROHF	Dense small-molecule accuracy reference. Closed-shell DF triples support requested-memory fast/blocked/direct/disk execution; open-shell triples support fast/direct but retain the dense spin-orbital integral floor. The dense CC iteration and the FNO setup remain production-size memory gates. Validated vs PySCF (uHa; conventional route to a few nHa) with ORCA 6.1 cross-checks.
A-CCSD(T)	method="ccsd", triples="A-CCSD(T)"	RHF	Closed-shell asymmetric/Lambda triples correction on CCSD amplitudes. This separate implementation remains dense and rejects bounded triples modes. The effective method and citation route are a-ccsd(t), with Kucharski-Bartlett 1998 and Crawford-Stanton 1998 references surfaced in output.
QCISD / QCISD(T)	"qcisd", "qcisd(t)" (also via citype=)	RHF	Closed-shell quadratic CI singles+doubles via exact monomial selection from the canonical CCSD residual. QCISD(T) uses the original Pople-Head-Gordon-Raghavachari E[T] + 2*E_ST triples convention on QCISD amplitudes. Pinned vs the in-repo spin-orbital oracle and out-of-process ORCA 6.1 RI-QCISD(T).
CCD / LCCD / LCCSD / CEPA(0..3)	"ccd", "lccd", "lccsd", "cepa(0)".."cepa(3)" (also via citype=)	RHF	Coupled-pair variants of the closed-shell DF-CCSD kernel (CCSDOptions field cc_variant): CCD freezes singles; LCCD/LCCSD linearize the amplitude equations (exact polynomial-stencil linearization of the canonical residual); CEPA(1..3) add Meyer’s pair-specific EPV shifts. CEPA validated to sub-uHa vs out-of-process ORCA 6.1 RI-CEPA/n (canonical orbitals). No (T); closed-shell only.
DLPNO-CCSD	"dlpno-ccsd"	RHF / UHF	Domain-based local pair natural orbital CCSD. Closed-shell: reduced-scaling local solver (pair classification, PAO domains, per-pair PNO solver). Open-shell (multiplicity > 1) auto-routes to UHF + the spin-orbital DLPNO-UCCSD pilot (Saitow 2017; O(N⁶), max_nbf-capped).
DLPNO-CCSD(T)	"dlpno-ccsd(t)"	RHF / UHF	Closed-shell: local solver plus local DLPNO-(T) (per-triple TNO domains), full-domain == canonical CCSD(T); defaults give MAE 0.30 kcal/mol vs canonical (0.166 with tcut_pno=1e-8 + triples_mode="exact"), cross-validated vs ORCA 6.1. Open-shell auto-routes to the UHF-reference spin-orbital DLPNO-UCCSD(T) pilot (Saitow 2017; exact vs the spin-orbital UCCSD(T) reference at full domains).
DLPNO-MP2	"dlpno-mp2"	RHF / UHF	Domain-based local pair natural orbital MP2 (Pinski 2015); closed-shell and open-shell DLPNO-UMP2 (UHF reference, Saitow 2017). Boys-localised occupieds, per-pair PNO virtual space; defaults recover >= 99.8 % of canonical RI-MP2 E_corr, thresholds -> 0 reproduces it to <= 1 uHa.
IC-CASPT2	"caspt2"	CASSCF/CASCI	Internally-contracted CASPT2, un-gated at v0.12.0. Large-basis direct active-CI path.
CASCI + CASSCF	"casci" / "casscf"	-	Multi-root CASCI (casci_options=CASCIOptions(nroots=N)) with state-averaged CASSCF (casscf_options=CASSCFOptions(nroots=N)); orbital-optimised. The CASSCF analytic nuclear gradient is FD-tight (~1e-7, default compute_wz=False path), validated in v0.15.0. State-averaged + open-shell CASSCF gradients fall back to FD. CASPT2/NEVPT2 gradients experimental (full-energy FD).
TDDFT (Casida + TDA)	run_tddft_tda / run_tddft_casida / run_job(tddft=True)	RHF/RKS/UHF/UKS	Vertical excitation energies, oscillator strengths, transition dipoles, dominant orbital transitions. Runner integration: `run_job(tddft=True, nto=True, tddft_type=”tda”
CIS / TDA	run_tddft_tda (TDA limit)	HF / MSINDO	Configuration-interaction singles; Tamm-Dancoff approximation. Finite-difference excited-state gradients (state-tracked).
Green’s function (GF2 / OVGF)	"ovgf"	HF / MSINDO	Quasiparticle IPs and EAs (result .ovgf); renormalised GF2 with full third-order self-energy + geometric screening auto-printed for small systems. Open-shell (UHF) propagator supported. MSINDO reference: vibeqc.semiempirical.methods.msindo.msindo_ovgf (renormalize=True for renormalised GF2).

Method	run_job(method=…)	Solver entry point	Notes
Full CI	"fci"	(dense eigh on the full determinant Hamiltonian)	Exact within the (active) orbital space; reference for the approximate solvers. Small active spaces only.
Selected CI (CIPSI)	"selected_ci"	solve_selected_ci	Iterative perturbative selection; target_size, pt2_threshold, optional PT2 correction.
DMRG	"dmrg"	solve_dmrg	Two-site sweep, MPS wavefunction, bond-dimension schedule. Minimal Python implementation, ≤12 orbitals.
Variational 2-RDM	"v2rdm"	solve_v2rdm	Exact small-active-space N-representable 1/2-RDM from the in-tree determinant Hamiltonian; Q/G SDP feedback remains unimplemented.
Transcorrelated CI	"transcorrelated_ci"	build_transcorrelated_hamiltonian + solve_selected_ci	Similarity-transformed Hamiltonian (Gaussian / Jastrow correlator) fed to selected CI.

• Active-space truncation: pass active_space=(n_orbitals, n_electrons) to run_job to restrict any solver to a frozen-core / CAS-style window. The runner projects the full MO-basis Hamiltonian onto the active block via Hamiltonian.active_space, which applies the standard CAS partition (lowest (nelec − n_elec)/2 orbitals as a doubly-occupied inactive core) with the proper frozen-core dressing, the effective one-electron term h̃_pq = h_pq + Σ_c (2⟨pc|qc⟩ − ⟨pc|cq⟩) and the constant E_core offset folded into the nuclear-repulsion term, so the reported energy is the full CAS total energy. The dressing is shared with the casci path, so fci/selected_ci/dmrg/v2rdm on a given active space agree with casci on the same window to numerical precision (E_FCI ≤ E_CAS ≤ E_HF). See python/vibeqc/solvers/ACTIVE_SPACE.md for the contract and tests/test_solvers_active_space_api.py for the variational-sandwich + cross-method coverage.

• Orbital source is decoupled, the solvers operate on an abstract Hamiltonian in an orthonormal MO basis; get_hf_orbital_provider is a convenience, not a requirement.

• Geometry optimisation, wavefunction methods optimise via numerical gradients (run_job(method="fci", optimize=True)); analytic gradients are roadmap.

• Parity, He / OH FCI parity tests and DMRG-vs-FCI cross-checks ship in tests/test_solvers_*.

Density fitting + RIJCOSX (v0.8.0)

JKBuilder polymorphic Fock build via three concrete kernels; see user_guide/density_fitting.md.

Kernel	Driver flags	When
FourIndexJKBuilder	(default)	small (≤250 BFs)
DFJKBuilder (RIJK)	density_fit=True, aux_basis="..."	medium (~250-1000 BFs), hybrid DFT
COSXJKBuilder (RIJCOSX)	density_fit=True, cosx=True, aux_basis="..."	large (>1000 BFs), hybrid DFT

• RIJK gradient: production-ready. The historical ~115 mHa glycine bug closed in v0.8.0; see user_guide/density_fitting.md.

• RIJCOSX SCF energy: validated to 0.26 mHa vs ORCA 6.1.1 on glycine / def2-TZVP. (An earlier revision of this bullet claimed the analytic gradient was “validated” on the strength of that energy comparison; the gradient claim was unproven and, pre-2026-07-29, wrong.)

• RIJCOSX analytic gradient: matches finite differences of the RIJCOSX energy surface to the neglected grid-motion band (~2e-4 Ha/bohr on H2O/def2-tzvp, ~3e-3 worst case OH/def2-svp; gate: tests/test_rijcosx_gradient_fd.py). Against ORCA 6.1.1 EnGrad on glycine/def2-TZVP: |grad| 0.08696 vs 0.08703 Ha/bohr, componentwise RMS 3.3e-3, max 1.1e-2; the residual is the documented fitted-Fock response term plus neglected grid-motion/weight derivatives (see compute_cosx_k_gradient_contribution notes in cpp/include/vibeqc/cosx.hpp).

• default_aux_basis_for(orbital_basis_name, kind="jk"/"ri") helper picks aux basis automatically.

Periodic SCF (native GDF / GPW / BIPOLE / Γ-CCM / χ-CCM)

Γ-CCM and χ-CCM[1] are distinct union-and-weight and finite-translation-group character approaches. The code selectors remain aiccm2026dev-a and aiccm2026dev-b.

Method	Driver	k-point support	Notes
RHF, Γ-only GDF	run_rhf_periodic_gamma_gdf	Γ, dim=1/3 (slab raises)	native vibe-qc J/K via Gaussian density fitting; no in-process PySCF
RKS / hybrids, Γ-only GDF	run_rhf_periodic_gamma_gdf(functional=…)	Γ, dim=1/3 (slab raises)	native libxc V_xc; hybrid exact exchange uses the functional’s HF fraction
KRHF multi-k GDF	run_krhf_periodic_gdf	Γ + multi-k, dim=1/2/3	native k-dependent GDF. On dim=2, an explicit full Gamma-centered (n1,n2,1) mesh selects the signed slab-truncated metric and rigorous 2D one-electron gauge; custom/IBZ meshes, smearing, restarts, and open shell stay closed. Closed-shell slab analytic gradients ship. Also reachable via run_periodic_job(jk_method="gdf", kpoints=...)
KRKS multi-k GDF	run_krks_periodic_gdf	Γ + multi-k, dim=1/2/3	native multi-k RKS / full-range hybrid path. The bounded dim=2 route has the same restrictions as KRHF and rejects range-separated functionals; closed-shell slab analytic gradients ship; PySCF / CRYSTAL are out-of-process references only
RIJCOSX periodic SCF	run_periodic_job(jk_method="rijcosx")	Gamma RHF; vacuum-padded Gamma RKS/UHF/UKS; true multi-k RHF/RKS/UHF/UKS	RI-J from the native GDF loop plus periodic COSX exchange (k_exchange="cosx") on true multi-k meshes (weighted full-BZ quadratures supported); one-cell tight-cell RKS/UHF/UKS fail closed rather than relabeling a GDF-only route
χ-CCM SCF / post-HF	run_aiccm2026dev_b_rhf/rks/uhf/uks, restricted and unrestricted MP2/CCSD(T)/PNO APIs; run_periodic_job(jk_method="aiccm2026dev-b")	real-space cyclic lattice extension, 3D absolute energies only	finite-character (Γ-centred character-mesh) CCM with four-centre, RI, and RIJCOSX restricted/unrestricted SCF plus 3D finite-torus correlation; every 1D/2D B backend fails closed pending a shared wire/slab Coulomb convention; local CC remains an O(N^6) correctness pilot, not production reduced scaling
χ-CCM RI-MP2	run_aiccm2026dev_b_mp2	finite cyclic mesh, 3D	momentum-conserving canonical RI-MP2 on the χ-CCM RI-RHF reference; external KMP2 parity; experimental
Γ-CCM / aiccm2026dev-a	vibeqc.periodic.ccm, method="aiccm2026dev-a"; run_ccm_rhf, run_ccm_rks, run_ccm_mp2, run_ccm_ump2, run_ccm_ccsd	real-space cyclic cluster extension (nrep)	union-and-weight/Wigner-Seitz integral-weighting CCM: HF/KS with the four-center construction, construction-specific RIJCOSX research, MP2/UMP2, CCSD(T), analytic gradients, properties, localization, and symmetry; experimental (every SCF driver emits AICCM2026DevAExperimentalWarning)
A-namespace neutral fitted-torus controls	run_ccm_rhf_gdf, run_ccm_rhf_direct, run_ccm_ri_mp2, run_ccm_ri_ccsd, run_ccm_uccsd, ccm_dlpno_*	separately declared finite-torus control operator	character/Bloch and real-Gamma evaluations plus restricted/unrestricted canonical and DLPNO correlation on the matching neutral control. These APIs are in vibeqc.periodic.ccm for historical reasons; they are not Γ-CCM or χ-CCM construction results; experimental (emit AICCM2026DevAExperimentalWarning)
Cell-resolved DF integral blocks	compute_2c_eri_lattice_blocks, compute_3c_eri_lattice_blocks, bloch_sum_*_eri_blocks, build_lpq_bloch_native	dim=1/2/3	native translation-resolved 2c/3c storage and Bloch/Lpq assembly for k-dependent GDF; Γ tensors are recovered by summing blocks
2D slab SCF (SLAB_EWALD_2D)	run_periodic_job(jk_method="auto") on a dim=2 system; vibeqc.slab_2d(a1, a2, atoms) to build one	Γ + multi-k, dim=2 only	Rigorous vacuum-free 2D Ewald (Parry 1975; de Leeuw and Perram 1979) for RHF / RKS / UKS. No vacuum gap: the third lattice column is synthesized bookkeeping and the total energy is invariant to it; E_nuclear is k-mesh independent. AUTO selects it for every dim=2 system. Explicit jk_method="gdf" is a bounded closed-shell RHF/RKS alternative with a signed slab-truncated fit and analytic gradients; BIPOLE / GPW / GAPW / RIJCOSX remain closed. Fermi-Dirac smearing and slab-GDF open shell are not shipped yet.
BIPOLE RHF / UHF / RKS / UKS	run_pbc_bipole_rhf, ..._uhf, ..._rks, ..._uks	Γ + multi-k, 3D through run_periodic_job	Production exact Ewald-J energy and finite-difference atomic-force route for closed- and open-shell periodic SCF. Fixed-cell atomic relaxation ships; variable-cell work fails closed. Analytic gradients remain a gated preview. The quartet multipole far-field prototypes are driver-unreachable: all four drivers default to False, and explicit True raises before setup
GPW RHF / ROHF / ROKS / UHF / RKS / UKS (v0.12.0)	run_periodic_job(jk_method="gpw")	Gamma supports all six methods; multi-k pure-DFT RKS/ROKS/UKS supports LDA/GGA/meta-GGA in molecular-limit and compact Bloch regimes through the public runner or the matching run_periodic_*_gpw_multi_k API; multi-k UHF/ROHF and hybrids remain gated	Production Gaussian Plane Waves route (serial), unified run_periodic_job user surface; ROHF and ROKS are maintained preview with one restricted orbital set and integer 2/1/0 occupations; GAPW all-electron augmentation; DFT+U for Gamma RHF/RKS/UHF/UKS plus multi-k RKS; D3-BJ dispersion; Gamma-point analytic gradient; FD Hessian; smearing. The MPI z-slab grid overlay (GpwJBuilder(mpi_aware=True)) is experimental: its multi-rank Hartree-J build was broken through v0.12.0, fixed post-release, pending validation on a real multi-rank run
RHF / RKS / UHF / UKS Ewald-3D (legacy)	run_*_periodic_*_ewald3d	Γ + multi-k	native debug path; not the CRYSTAL-parity target
Multi-k UHF / UKS via GDF	run_kuhf_periodic_gdf, run_kuks_periodic_gdf; public runner	Γ + multi-k, dim=1/3	Public GDF open-shell route. Slab open shell remains fail-closed.
ROHF periodic, Ewald-3D	run_rohf_periodic_gamma_ewald3d, run_rohf_periodic_multi_k_ewald3d	Γ + multi-k, dim=3	Standalone HF drivers with the shared Roothaan coupling and integer 2/1/0 occupations; not wired through run_periodic_job
ROHF periodic, native GDF	run_periodic_job(method="ROHF", jk_method="gdf"), run_krohf_periodic_gdf	Γ (a (1,1,1) mesh) + full multi-k, dim=3	Public and standalone density-fitted ROHF on the per-(k_i,k_j) cderi cache: same J / per-spin K / exxdiv='ewald' machinery as the PySCF-pinned KRHF/KUHF drivers, with the Roothaan coupling as the only new step. Exchange contracts against the occupied MO blocks. Multiplicity 1 reproduces run_krhf_periodic_gdf exactly; Li/STO-3G Γ is +2.86e-5 Ha from PySCF KROHF/GDF, collapsing to +2.2e-7 Ha with the rsgdf mesh. ROKS, smearing, 2D slabs, gradients, optimization, restarts, COSX and ibz_native remain fail closed
ROHF / ROKS periodic, GPW	run_periodic_job(method="ROHF", jk_method="gpw"), run_periodic_job(method="ROKS", functional=..., jk_method="gpw"), run_periodic_rohf_gpw, run_periodic_roks_gpw, run_periodic_roks_gpw_multi_k	ROHF: Gamma only; ROKS: Gamma plus full multi-k pure-DFT meshes; dim=3	Maintained-preview restricted-open-shell route: GPW Hartree J, per-spin exact K where required, spin-polarised XC for ROKS, the Ewald one-electron/nuclear gauge, and complex-safe Roothaan coupling. Unsupported dimensions, gradients, GAPW, multi-k hybrids, range-separated ROKS, and electronic smearing fail closed; smearing_alpha is nuclear smoothing
Atomic gradients (periodic)	route-specific FD forces; compute_gradient_periodic_* previews	Γ + multi-k by route	BIPOLE production forces use finite differences of the executed energy; analytic coverage is route- and envelope-specific and remains preview where documented
Periodic force-virial diagnostic	compute_stress_tensor	Γ + multi-k	Diagnostic only; not the periodic stress. BIPOLE/GDF variable-cell optimization fails closed

Reference benchmark: ΔE = -6.8e-12 Ha for MgO/sto-3g/Γ RHF vs out-of-process PySCF.pbc.GDF. Multi-k KRHF / KRKS GDF is now native, the multi-k Ewald-gauge fix brings a multi-k mesh to within 0.000 mHa of the Γ-point energy in the molecular limit; there is no in-process PySCF backend.

See user_guide/multi_k_scf.md for the full multi-k story including the dense-Lpq RAM ceiling caveat.

Semiempirical methods + MLIP (v0.11.0-v0.12.0)

Method	run_job(method=…)	Coverage	Notes
MSINDO	"msindo"	INDO H-Xe (Z 1-54); NDDO H, Li-F, Na-Cl closed shell	Independent MSINDO INDO/NDDO implementation. Native C++ production routes cover supported molecular RHF/UHF energy and closed-shell analytic gradients. CCM energy/gradients use C++ for H-Kr and the deterministic Python reference for Rb-Xe; a selected native calculation does not fall back after failure. Python also remains for reference/orchestration paths including excited-state/root-tracking workflows.
GFN2-xTB	"gfn2_xtb"	H-Rn (Z 1-86)	Gated experimental tight-binding semiempirical route; molecular H0, shell SCC, third-order, AES, analytic gradients, and scoped post-SCF native D4 are implemented. Periodic AES images and external xtb parity remain production gates.
MACE MLIP (v0.11.x)	"mace" for molecules; direct periodic drivers	Registered MACE-MP/MPA-0 materials models and MACE-OFF23 organic models	Optional mace-torch engine on Python <= 3.13. Molecular dispatch supports energy, forces, optimization, and NEB. Direct periodic energy/forces support 1D, true 2D slabs, and 3D; vibeqc.mlip.mace.optimize_periodic_mace_positions provides fixed-cell relaxation with frozen atoms. Stress and vibeqc.mlip.mace.optimize_periodic_mace_cell are 3D-only. run_periodic_job(method="mace") is not supported. Model-specific energy scales are not electronic totals.

Effective core potentials

libecpint 1.0.7 vendored. Heavy-element chemistry (d-block, lanthanides, actinides) reachable without all-electron basis.

ECP library	Family	Coverage
ecp10mdf	Stuttgart-Köln MDF, 10-electron core	post-K (rows 4+)
ecp28mdf	Stuttgart-Köln MDF, 28-electron core	post-Cd
ecp46mdf	Stuttgart-Köln MDF, 46-electron core	post-Hg
ecp60mdf	Stuttgart-Köln MDF, 60-electron core	f-block (post-Yb)
ecp78mdf	Stuttgart-Köln MDF, 78-electron core	actinides
lanl2dz	Hay-Wadt LANL	post-Na (rows 3+)

Two recipes: manual ECPCenter (always shipped) and vq.auto_ecp_centers(mol, basis_name) (shipped on main). See user_guide/ecp.md for the full story.

Analytic nuclear gradients are ECP-aware on all four molecular drivers (GradientOptions.ecp_centers / ecp_library; the ASE calculator and optimize=True wire them automatically): Z_eff nuclear pieces plus dV_ECP/dR via libecpint first derivatives, analytic-vs-FD pinned to <= 1e-5 Ha/bohr. See user_guide/ecp.md § Gradients.

Reference: Pt UHF/LANL2DZ = −118.227 Ha (22 BFs, 125 SCF iters).

SCF convergence aids

Aid	API	Coverage	Notes
DIIS extrapolation	*_options.use_diis	molecular + periodic Γ + multi-k	default on, ~10× iter speedup
EDIIS + EDIIS+DIIS hybrid (v0.8.0)	*_options.scf_accelerator=SCFAccelerator.EDIIS_DIIS	molecular + C++ direct-truncated periodic + Python Γ-Ewald (RHF/RKS/UHF/UKS)	flagship for stiff convergence; rollout to Python multi-k Ewald / BIPOLE / GDF in progress
KDIIS (Kollmar)	*_options.scf_accelerator=SCFAccelerator.KDIIS	molecular + C++ Γ-only periodic + Python Γ-Ewald (RHF/RKS/UHF/UKS)	orbital-rotation gradient error; ORCA’s opt-in !KDIIS; multi-k path needs per-k MO-basis design
ADIIS (Augmented Roothaan-Hall)	*_options.scf_accelerator=SCFAccelerator.ADIIS	molecular + C++ direct-truncated periodic + Python Γ-Ewald	EDIIS sibling, no per-iter energy needed
Dynamic damping (Zerner-Hehenberger 1979)	*_options.dynamic_damping, dynamic_damping_min/_max	molecular + C++ direct-truncated periodic + Python Γ-Ewald (RHF/RKS/UHF/UKS)	adaptive density mixing α; composes freely with the accelerator family
Damping (static)	*_options.damping	all	density mixing
CRYSTAL-style FMIXING	*_options.fock_mixing; run_periodic_job(fmixing_percent=30)	molecular + native periodic direct + supported GDF routes	Fock/KS matrix mixing; FMIXING 30 = 0.30, separate from density damping; GDF exceptions are fail-closed or AUTO-filtered as documented in scf_convergence.md
Saunders-Hillier level shift	*_options.level_shift	molecular + periodic Γ + multi-k, with route-dependent GDF coverage	Phase C1a; GDF exceptions are fail-closed or AUTO-filtered as documented in scf_convergence.md
Level-shift warm-up/restart	*_options.level_shift_warmup_cycles; run_*_periodic_gdf(..., level_shift_warmup_cycles=...)	native Γ-GDF + Γ KRHF/KRKS bridge	-1 auto, 0 persistent shift, positive values restart unshifted after that many cycles
Quadratic (“Newton”) SCF	*_options.quadratic_fallback_iter	molecular + periodic Ewald Γ/multi-k	Phase C1c, fallback for small-gap systems; experimental aiccm2026dev-b routes require 0 and fail closed on activation
Fermi-Dirac smearing	*_options.smearing_temperature; `run_periodic_job(smearing_temperature=”auto”	“metal”	…); vq.SmearingOptions, vq.apply_smearing(), vq.resolve_smearing_temperature()`
Periodic density mixers (Anderson / Broyden / Kerker, v0.14)	run_periodic_job(..., density_mixer=...); run_rks_periodic_scf(...) / run_rks_periodic_multi_k_ewald3d(...)	closed-shell explicit-kpoint GDF dispatch + lower-level multi-k RKS Ewald	Kerker preconditions the density residual without moving the SCF fixed point; unsupported BIPOLE, GPW/GAPW, open-shell, and implicit-Gamma routes fail closed
auto_optimize_truncation	PeriodicRHFOptions(auto_optimize_truncation=True)	periodic	default on; jointly optimises lattice cutoffs + Schwarz screening

XC functionals (v0.8.0 expanded)

Resolved through libxc 7.0.0; see user_guide/functionals.md. Short aliases the resolver knows:

Alias	Type	HF-exchange	libxc id
lda / svwn	LDA	0 %	1 + 7
pbe	GGA	0 %	101 + 130
blyp	GGA	0 %	106 + 131
b3lyp (= b3lyp5)	hybrid	20 %	475 (VWN5, the ORCA / TURBOMOLE / ADF / CRYSTAL convention)
b3lyp/g (= b3lypg)	hybrid	20 %	402 (Gaussian/VWN-RPA variant, what Gaussian / PySCF / Psi4 mean by the bare name)
pbe0 / pbeh	hybrid	25 %	406
pw1pw	hybrid	20 %	weighted-sum
hse06	range-sep hybrid	25 % SR	425
vv10 (v0.14)	GGA + nonlocal	0 %	255
wb97x-v (v0.14)	range-sep + VV10	100 % LR	466
wb97m-v (v0.14)	range-sep meta-GGA + VV10	100 % LR	531
r2scan01 (v0.14)	meta-GGA	0 %	642 + 645
revdsd-pbep86 (v0.14)	double hybrid (D4)	69 %	101 + 132

Plus everything libxc accepts directly + custom weighted-sum strings (PW1PW pattern: "0.2*HF + 0.8*GGA_X_PW91, GGA_C_PW91").

B3LYP convention: vibe-qc ships the ORCA definition, bare b3lyp is libxc id 475 (VWN5), the same flavor ORCA, TURBOMOLE, ADF, CRYSTAL, and CP2K mean by the name; Gaussian, libxc, PySCF, Psi4, NWChem, and Q-Chem mean the VWN-RPA variant (id 402), which vibe-qc spells b3lyp/g / b3lypg. The flavor gap is ~6.8 mHa on H₂/STO-3G, ~10-15 mHa per heavy atom. v0.12.0 added the explicit b3lyp5 / b3lypg spellings and a measured cross-code audit. See user_guide/functionals.md for the camp table, the measured values, and why there is no b3lyp3 alias.

Ewald summation (Phase 12e, mostly shipped)

See user_guide/ewald.md for the math

• API.

Sub-phase	Scope	Status
12e-a	Classical Ewald nuclear lattice sum (CoulombMethod.EWALD_3D)	✅
12e-b	erfc-screened nuclear attraction compute_nuclear_erfc_lattice	✅
12e-c-1	Gaussian-charge Ewald V(g) via grid integration	✅
12e-c-2	erfc-screened ERIs for Ewald short-range J/K	✅
12e-c-3a	FFTW3 build dep + solve_poisson_*	✅
12e-c-3b	build_j_long_range + auto_grid	✅
12e-c-3c	Quartet multipole far-pair replacement	Fail-closed research prototype
12e-c-4	End-to-end EWALD_3D SCF dispatch (RHF/RKS/UHF/UKS, Γ + multi-k)	✅

Madelung-constant validation:

Crystal	M reproduced	Reference
NaCl rocksalt	1.7475645946 to 1e-8	1.7475645946…
CsCl	1.762674773 to 1e-8	1.762674773…
ZnS zincblende	1.6380550533 to 1e-9	1.6380550533…
Simple-cubic jellium	1.4186487 to 1e-6	1.4186487 (Nijboer-De Wette 1957)

External data fetcher (vqfetch, v0.8.0)

Pulls structures + reference data from public databases on demand. Per-record provenance + license preserved.

Subcommand	Source	Default license
vqfetch optimade --formula MgO	OPTIMADE federation	per-provider
vqfetch mp --id mp-1265	Materials Project	CC-BY 4.0
vqfetch cod --id 1011027	COD	CC0 / public domain
vqfetch canonical <slug>	(5 round-trip-verified slugs)	(per primary)
vqfetch reference --cas 7732-18-5	NIST CCCBDB	US Govt public domain

See user_guide/external_structures.md

• user_guide/reference_data.md. End-to-end planetx round-trip: MgO sto-3g RKS-LDA E = −950.4204308512 Ha (13 SCF iters).

Job queue (vq v0.5.6, v0.8.0)

SSH-backed remote job submission co-shipped in vibe-queue/. Cgroup-v2 enforcement, web dashboard, pause/resume, multi-venv --branch routing. See user_guide/queue.md.

Capability	Since
Local queue + CLI + daemon + JobSpec v1 + systemd unit	v0.1.0
Cross-machine SSH submit + ~/.config/vq/config.toml + vq fetch	v0.2.0
Resource watchdog (--mem-mb, --wall-time-seconds, OOM_KILLED / STARVED / TIME_EXCEEDED)	v0.3.0
Cgroup-v2 enforcement (systemd-run scope), pgid-based daemon recovery	v0.4.0
ABORTED_BY_QUEUE terminal state	v0.4.1
Read-only web dashboard (FastAPI + htmx)	v0.5.0
vq pause / vq resume + bearer-token auth + write API	v0.5.1
--all flag on pause/resume + queue-wide POST /api/v1/queue/*	v0.5.2
CRYSTAL14 + PROPERTIES14 reachable through dispatched jobs	v0.5.3
Parallel CRYSTAL14 (Pcrystal/Pproperties default --np 14) + clean systemd PATH drop-in	v0.5.4-5
Multi-venv routing via --branch for vibe-qc dev/release dispatch	v0.5.6

Properties

Property	API	Methods	Notes
Mulliken charges	mulliken_charges	RHF / UHF / RKS / UKS	atomic populations
Löwdin charges	loewdin_charges	all	symmetric-orth populations
Mayer bond orders	mayer_bond_orders	all	per-pair indices
Dipole moment	dipole_moment	all	with optional origin
Natural orbitals	natural_orbitals	all	for post-SCF analysis
Static polarizability α	dipole_polarizability_rhf	RHF (closed-shell)	via CPHF, Phase 17b-1; UHF/KS roadmap
Vibrational frequencies (FD)	compute_hessian_fd + HessianResult.frequencies_cm1	all	FD on analytic gradient; trans/rot projection
Vibrational frequencies (analytic)	compute_hessian_rhf_analytic	RHF	CPHF + libint deriv_order=2; Phase 17b-3
IR intensities	ir_intensities	all	dipole derivatives along normal modes
Thermochemistry (ZPE / U / H / S / G / Cv)	compute_thermochemistry	all	rigid-rotor + harmonic-oscillator + ideal-gas
D3(BJ) dispersion	compute_d3bj	all	Grimme D3 with Becke-Johnson damping
D4 dispersion (v0.8.0)	compute_d4	all	Caldeweyher-Bannwarth-Grimme 2019
Cube file output	write_cube	all	density / orbital / spin density
Molden file export	write_molden	RHF / UHF / RKS / UKS	verified by PySCF round-trip
Periodic band structure	band_structure	periodic SCF	k-path sampling
Periodic density of states	density_of_states	periodic SCF	Gaussian broadening on a sampled mesh
Atomisation energy	run_job(..., atomization=True) (vibeqc.atomization.atomization_energy)	HF / DFT	per-element free-atom references at the same level, cached; main-group H-Kr. MSINDO reports its binding energy by default.
Green’s function IP / EA	run_job(method="ovgf") → result.ovgf; MSINDO: msindo_ovgf	HF / MSINDO	quasiparticle ionisation potentials and electron affinities (.ip_homo_ev / .ea_lumo_ev on the MSINDO result)
MPI substrate (v0.12.0)	mpi4py optional extra; vibeqc.mpi helpers	experimental GPW z-slab overlay plus low-level collectives	install with [mpi] extra. Production distributed HF / DFT / MP2 drivers are not wired yet; see MPI Parallelization. The GPW z-slab grid overlay is experimental (multi-rank Hartree-J build broken through v0.12.0, fixed post-release; pending real multi-rank validation)
COOP/COHP (v0.15.0)	compute_coop_cohp	periodic SCF	energy-resolved Crystal Orbital Overlap/Hamilton Population; C++ kernels, QVF dos.coop/dos.cohp, plotters, vibeqc coop CLI
Periodic Mayer bond orders (v0.15.0)	periodic_mayer_bond_orders	periodic SCF	k-space generalisation; QVF bond_orders
QTAIM (v0.15.0)	vibeqc.qtaim.qtaim_analysis	all	critical-point search + bond-path tracing; analytic C++ Hessian; QVF topology.qtaim
Fat bands (v0.15.0)	band_structure_projected	periodic SCF	Mulliken-projected band weights; QVF bands projections
Wiberg bond indices + delocalization index	vibeqc.bond_analysis.wiberg_bond_orders / .delocalization_index / .bond_order_summary	all	Löwdin-basis Wiberg 1968 index; AO-approximated DI; auto-emitted in .population.{txt,json}
NPA charges + NBO search	vibeqc.nbo.npa_charges / .nbo_search / .donor_acceptor_analysis	all	Weinhold NPA (auto-emitted in .population.*); BD/LP/CR/BD*/RY* classification; E(2) donor-acceptor
Energy decomposition analysis	vibeqc.eda.eda_lmo / .eda_morokuma	HF / DFT	LMO-EDA (Su-Li 2009) + Morokuma 1971 two-fragment decomposition
Orbital entanglement	vibeqc.entanglement.entanglement_from_density / .single_orbital_entropy / .mutual_information	all	single-orbital entropy, mutual information, entanglement bond orders, correlation clusters

Input / output

Capability	API	Notes
High-level “run-a-job” driver	run_job / run_periodic_job	dispatches to right SCF driver, writes .out + .molden, runs BFGS if asked
MPI substrate (v0.12.0)	pip install -e '.[mpi]'	optional mpi4py extra; low-level collectives plus experimental GPW grid overlay. Production MPI strategy is tracked in MPI Parallelization
Formatted SCF log	format_scf_trace, log_scf_trace	banner, iteration trace, energy components, orbital table, HOMO-LUMO gap
Molden export	write_molden	verified by PySCF round-trip
Geometry trajectory	run_job(..., optimize=True)	ASE .traj file
XYZ / Extended-XYZ load	Molecule.from_xyz / from_xyz	molecular XYZ by default; periodic=True reads Extended-XYZ Lattice / pbc into PeriodicSystem; symmetrise=True returns SymmetriseResult
POSCAR load / save	read_poscar, write_poscar	VASP 5 format
CIF load / save	read_cif, Crystal.from_cif, write_cif	cell parameters + atom-site loops; symmetry operations expand asymmetric-unit sites
Cube load / save	read_cube, write_cube	volumetric data
BXSF (band structure)	write_bxsf	XCrySDen 3D Fermi-surface format

Basis sets

• 239 bundled Gaussian .g94 basis files in the runtime basis/ library: 90 libint-inherited standard files plus 149 vibe-qc custom / BSE-derived overlay files, with matching QVF-Basis sidecars for every set.

• Custom and BSE-derived sets in python/vibeqc/basis_library/custom/: pob-TZVP, pob-DZVP-rev2, pob-TZVP-rev2 (Bredow-group periodic-tuned), plus the BSE-sourced and release-paper reproduction bases.

• CRYSTAL-format parser, imports arbitrary CRYSTAL per-element basis files; converts to libint-compatible .g94. CRYSTAL INPUT ECP-block parsing is available for basis/ECP migration work.

• ECP basis sets, fully wired through libecpint (see ECP section above).

• Basis-set optimisation (v0.14), re-optimise a basis set’s exponents and coefficients against a molecular energy via the analytic-gradient BDIIS recipe (optimize_molecular_basis); see user_guide/basis_optimization.md.

• Basis inventory and attribution documented in docs/license.md, including the libint-inherited files, the Bredow-group pob-* bases, and the BSE-derived custom overlay.

Crystal / lattice infrastructure

• spglib integration: Crystal, analyze_symmetry, detect_spacegroup, symmetrise, to_primitive, irreducible_kpoints.

• CIF, POSCAR, and periodic Extended-XYZ input, with opt-in symmetrise=True standardisation into a calculation-ready PeriodicSystem.

• Monkhorst-Pack k-mesh generation with IBZ reduction, density-based auto-mesh helpers, and on-the-fly generalized regular grids via KPoints.optimal.

• Standardise-then-compress helpers for one-electron lattice integrals: compute_overlap_lattice_symmetrised_with_orbits plus kinetic / nuclear siblings rebuild the basis on the cleaned cell and return the SYM3a orbit-compressed storage view.

• 1D / 2D / 3D PeriodicSystem geometry.

• Hexagonal and other skew-cell geometry support; the native EWALD_3D Hartree path uses the analytical AO-pair FT on the full reciprocal metric.

Validation

Test class	Count	Level
Molecular 1e integrals vs PySCF	24	machine precision
RHF / UHF / RKS / UKS energies vs PySCF	59	machine precision (HF), grid-accuracy (DFT)
MP2 / UMP2 / RI-MP2 / SCS-MP2 / SOS-MP2 / B2PLYP vs PySCF	55	1e-9 Ha (MP2 family) / 1e-7 Ha (B2PLYP)
Gradients (HF, DFT) vs FD / PySCF	17	1e-6 Ha/bohr
FD Hessian skeleton vs FD-on-gradient	8	1e-4 to 1e-3
Analytic RHF Hessian vs PySCF analytic	8	2.5e-9 Ha/bohr², freqs <0.01 cm⁻¹
FD Hessian + IR + thermochemistry vs PySCF	51	1e-7 Ha
CPHF + polarizability vs PySCF FD	11	1e-5 a.u.
Periodic machinery (invariants, molecular limit, Bloch folding)	76	machine precision
Periodic SCF convergence aids	27	per-test scoped
Periodic native GDF/FFTDF parity	planned	compare parsed out-of-process CRYSTAL and PySCF outputs
Multi-k KRHF/KRKS native parity	planned	no in-process PySCF backend
JKBuilder + RIJCOSX vs ORCA 6.1.1 (v0.8.0)	curated	RIJCOSX SCF energy max |Δ| = 0.26 mHa on glycine def2-TZVP (energy only; gradient parity tracked separately, see § Density fitting + RIJCOSX)
vqfetch acceptance harness (v0.8.0)	5 structures + 8 molecules	round-trip end-to-end
Crystal / POSCAR / basis parsing	18	-
Bundled basis-library integrity	239 .g94 files + 13 ECP sidecars	generated QVF sidecars, provenance / citation coverage, ECP split, privacy checks

Plus the full regression suite at examples/regression/ (since v0.7.2 Boys’ Crucible) covers the cross-code parity matrix (vibe-qc vs PySCF vs ORCA) on a curated S22 / X23 / pob-TZVP test set.

Full pytest suite: ~1800 test functions across ~190 files covering the molecular, periodic, wavefunction-solver, and output stacks; runs in ~3-4 minutes on an M-class MacBook (faster with pytest -n auto).

Known issues

See the warning admonition on docs/index.md for the live open-bugs list. Highlights:

• Periodic GDF parity, Γ-only and multi-k µHa parity vs PySCF on LiH FCC shipped at v0.11.0 (Sun’s Stingray). Mixed Density Fitting (MDF) shipped at v0.13.0, closing the all-electron GDF accuracy floor (Sun-Berkelbach 2017) for MgO. Dense-crystal periodic-DFT XC error fixed in v0.15.0 (cross-cell density + SCF convergence).

• Multi-k dense Lpq RAM ceiling (multi-TB on production systems). Streaming-Lpq tracks with the periodic GDF work.

• Si-diamond / C-diamond RKS/PBE oscillation on RI path – SCF-settings investigation ongoing (damping/DIIS interplay, not algorithmic). Density mixers (Anderson/Broyden) shipped in v0.14.0 as an alternative convergence path.

• BIPOLE gradients: production forces finite-difference the supported exact SCF energy. Corrected- and legacy-gauge analytic implementations remain gated previews with a narrower maintained regression envelope; they are not evidence that the fail-closed quartet multipole gradient is integrated.

• Open-shell UHF / UKS analytic gradient on f-shells with two or more different second-row elements still disagrees with ORCA. Closed-shell direct gradients now auto-route through the DF gradient path; the open-shell auto-route is queued.

• AUTO initial guess (SAP on closed-shell light-atom systems) oscillates on long n-alkanes and on H2CO + PBE. Pin InitialGuess.SAD to work around.

• pob-TZVP / pob-TZVP-rev2 missing Ne entry.

• Heavy-atom basis-load test OOMs a 16 GB laptop in batch mode; route via vq submit to a larger box.

• ωB97X / ωB97X-D UKS on orbital-near-degenerate radicals needs a level shift to converge.

• 3c composite methods are calibrated on molecular systems; the periodic flavours need recalibration before being trusted.

The B3LYP local-correlation convention (bare b3lyp = VWN5 / ORCA definition since v0.8.0; explicit b3lyp5 / b3lypg spellings since v0.12.0) is documented in user_guide/functionals.md as informational, not a bug, both flavors are correct B3LYPs; codes differ in which one the bare name means.

---

[1]

Γ-CCM and χ-CCM are distinct CCM construction approaches: union-and-weight/Wigner-Seitz integral weighting and finite-translation-group characters, respectively. A declared common exchange-q=0 convention is a comparison constraint, not an identification of the constructions. Their distinction is not a choice of Coulomb kernels, and equality for a specified operator and route must be established rather than inferred from the labels.