Feature matrix

The capability matrix as of v0.15.0 (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)	(roadmap M6)	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	Canonical CCSD (DF or exact-integral) plus the perturbative triples correction; closed- and open-shell (UCCSD(T) / ROHF-CCSD(T)). Frozen natural orbitals (FNO) available for closed-shell (DF only). 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. 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 + analytic gradient: validated to 0.13 mHa vs ORCA 6.1.1 on glycine / def2-TZVP.

• 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=1/3 (slab raises)	native k-dependent GDF; Γ delegates to the Γ-GDF path, any other Monkhorst-Pack mesh runs the full multi-k loop. Also reachable via run_periodic_job(..., gdf_kmesh=(n,n,n))
KRKS multi-k GDF	run_krks_periodic_gdf	Γ + multi-k, dim=1/3 (slab raises)	native multi-k RKS / hybrid path; PySCF / CRYSTAL are out-of-process references only
RIJCOSX periodic SCF	run_periodic_job(jk_method="rijcosx")	Gamma RHF; 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; one-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.
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.
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, and all bulk J/K builders (GDF / BIPOLE / GPW / GAPW / RIJCOSX) fail closed on a slab. Analytic gradients, Fermi-Dirac smearing, and UHF on a slab are not shipped yet.
BIPOLE RHF / UHF / RKS / UKS	run_pbc_bipole_rhf, ..._uhf, ..._rks, ..._uks	Γ + multi-k	Production exact Ewald-J energy route for closed- and open-shell periodic SCF. Multi-k KS analytic gradient with space-group symmetry and multipole L=3 (v0.12.0). The multipole far-field branch remains experimental/off by default
GPW RHF / UHF / RKS / UKS (v0.12.0)	run_periodic_job(jk_method="gpw")	Γ-only (RKS/UKS need functional=); multi-k pure-DFT RKS via run_periodic_rks_gpw_multi_k (LDA/GGA/meta-GGA; molecular-limit + compact Bloch regimes) and multi-k pure-DFT UKS via run_periodic_job(method="UKS", kpoints=...) or run_periodic_uks_gpw_multi_k (LDA/GGA/meta-GGA); multi-k UHF/hybrids not wired (per-k exact exchange)	Production Gaussian Plane Waves route (serial), unified run_periodic_job user surface; GAPW all-electron augmentation; DFT+U for Γ RHF/RKS/UHF/UKS plus multi-k RKS; D3-BJ dispersion; Γ-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	-	-	roadmap (GDF parity chain closed at v0.11.0; multi-k UHF/UKS GDF extension queued)
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, GPW	run_periodic_rohf_gpw	Γ only, dim=3	Implemented standalone HF route: GPW Hartree J, per-spin exact K, Ewald one-electron/nuclear gauge, and the shared Roothaan loop. No GDF/BIPOLE/GAPW, periodic ROKS, or electronic smearing; smearing_alpha is nuclear smoothing
Atomic gradients (periodic)	compute_gradient_periodic_*	Γ + multi-k	Phase G1; ships for RHF / UHF / RKS / UKS
Periodic force-virial diagnostic	compute_stress_tensor	Γ + multi-k	Diagnostic only; not the periodic stress. Use route-specific FD strain/cell optimizers for cell relaxation

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, closed-shell analytic gradients, CCM energy/gradients, and COSMO helper kernels; Python 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"	universal	Machine-learning interatomic potential via mace-torch.

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 Γ + multi-k	Phase C1c, fallback for small-gap systems
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	Saunders-Dovesi multipolar splitting	⏳ in progress
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 max |Δ| = 0.13 mHa on glycine def2-TZVP
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 analytic gradients: the corrected-gauge analytic gradient landed 2026-06-17 for all four methods (RHF/UHF/RKS/UKS) at both Γ and multi-k, FD-validated and un-refused. The legacy-gauge analytic preview (shipped at v0.12.0, Knuth’s Beaver) remains available. Production forces remain the exact FD path by maintainer decision.

• 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.

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[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.