Experimental

vibe-qc ships a handful of features behind an experimental gate. They are reachable, but not yet production-certified and subject to change without the usual deprecation cycle. Each one emits an ExperimentalWarning when used.

What’s in this section

  • The feature catalog is the complete table of every gated feature, its opt-in, its caveat, and its quantitative-status column. Start there if you want to know what’s gated and why.

  • Basis set development, developer documentation for the basis-set optimiser toolchain, design notes, and verification reports.

  • AICCM, the ab-initio cyclic cluster model, both Γ-CCM (aiccm2026dev-a, union-and-weight/Wigner–Seitz integral weighting) and χ-CCM[1] (aiccm2026dev-b, finite-translation-group characters).

Basis set development

Basis set development

AICCM: ab-initio cyclic cluster model

The cyclic cluster model is vibe-qc’s signature real-space approach to periodic systems. Two independent implementations are maintained while the common limit is being established:

  • aiccm2026dev-a, the union-and-weight Gamma-supercell CCM line (vibeqc.periodic.ccm). Its construction methods are HF, KS, MP2, UMP2, and CCSD(T), with analytic gradients and derivable properties. The same namespace contains neutral fitted-torus UCCSD(T) and DLPNO controls that are not assigned a Γ-CCM or χ-CCM identity.

  • aiccm2026dev-b, χ-CCM, the finite-character (Γ-centred character-mesh) CCM line (vibeqc.periodic_aiccm2026dev_b). It uses the explicit Γ-centred character net, with 3D RHF/RKS/UHF/UKS plus RI-MP2 and local-PNO CCSD(T). Every 1D/2D absolute-energy backend fails closed.

Open-shell capabilities across both lines are documented in Open-shell AICCM.

AICCM reference

AICCM tutorials

AICCM experimental

AICCM examples

The runnable examples live under examples/periodic/:

  • aiccm2026dev_a_demo.py, Γ-CCM union-and-weight stack: 8-fold ERI symmetry check on 1-D/2-D/3-D lattices and the HF→MP2→CCSD(T) correlation ladder. It also reports the neutral four-center Madelung-background diagnostic as a separate control.

  • aiccm2026dev_b_demo.py, χ-CCM: exercises all three ER backends in 3D; 1D/2D invocations demonstrate the intentional fail-close and do not return absolute energies.

  • aiccm2026dev_b_mp2.py, canonical RI-MP2 in 3D.

  • aiccm2026dev_b_local_correlation.py, DLPNO-MP2 and DLPNO-CCSD(T) on the χ-CCM finite torus.

  • aiccm2026dev_diamond_bonds_bands_compare.py, side-by-side diamond HF/KS property bundles and localized-orbital QVF archives; it records the cross-approach comparison as not-defined and emits no delta.

  • benchmark_aiccm2026dev_b.py, H4 convergence comparison against the historical and Γ-CCM weights.

The B/CRYSTAL fleet and future Γ-CCM/χ-CCM study inputs live under aiccm-2026/.

AICCM documentation map

you want to…

read this

Run a minimal example

Quickstart

Run your first Γ-CCM calculation

Γ-CCM tutorial

Run your first χ-CCM calculation

χ-CCM tutorial

See all Γ-CCM methods and routes

Γ-CCM reference

See all χ-CCM methods, backends, and caveats

χ-CCM user guide

Compare Γ-CCM UHF/UMP2, neutral-control UCCSD(T), and χ-CCM open-shell APIs

Open-shell AICCM

Study Γ-CCM and χ-CCM side by side (no current approach delta)

Cross-stream comparison

Choose the right basis set

Basis sets for AICCM

Debug a failing calculation

Troubleshooting

Generate orbital/density visualizations

Visualization

Understand the broad CCM concept

CCM tutorial

Understand the χ-CCM derivation

χ-CCM derivation

Understand the theory (Γ-CCM paper)

Γ-CCM theory paper

See also