Diamond Γ-CCM / χ-CCM bond and band comparison

This experimental input compares the two independent CCM development representations on primitive diamond:

  • aiccm2026dev-a, Γ-CCM, the direct-space Gamma-supercell CCM stream in vibeqc.periodic.ccm.

  • aiccm2026dev-b, χ-CCM[1], the finite-character (Γ-centred character-mesh) CCM stream in vibeqc.periodic_aiccm2026dev_b.

The input is:

python examples/periodic/aiccm2026dev_diamond_bonds_bands_compare.py \
  --route both \
  --basis sto-3g \
  --functional pbe \
  --backend four_center \
  --extension 2 2 2

It writes all files below output/aiccm-diamond-compare/ by default:

  • diamond-aiccm2026dev-a-vs-b-summary.json, with energies per primitive cell, finite-net gaps, Mulliken charges, C-C Mayer bond orders, band metadata, and occupied-localization diagnostics.

  • diamond-aiccm2026dev-a-rhf.qvf and diamond-aiccm2026dev-b-rhf.qvf, containing the primitive structure, the HF band path, and QVF bond connectivity.

  • diamond-aiccm2026dev-a-rks.qvf and diamond-aiccm2026dev-b-rks.qvf, the matching KS-DFT band and bond archives.

  • diamond-aiccm2026dev-a-rhf-localized.qvf and diamond-aiccm2026dev-b-rhf-localized.qvf, finite-supercell localized occupied orbitals for visualization.

  • PNG band plots when matplotlib is installed.

The default is a smoke calculation, not a publication benchmark. Increase the cyclic extension and use a solid-state basis such as a pob basis before quoting numbers. The band path is obtained from the converged finite-torus Fock blocks: it is exact at the folded character net and an interpolation between those points. Converge it with respect to --extension.

Optional local-PNO summary

Add --with-b-pno-mp2 to run the χ-CCM local-PNO MP2 pilot after the SCF steps:

python examples/periodic/aiccm2026dev_diamond_bonds_bands_compare.py \
  --route b \
  --backend ri \
  --extension 2 2 2 \
  --with-b-pno-mp2

This writes diamond-aiccm2026dev-b-dlpno-mp2.json with PAO rank, translation-pair reduction, and local-PNO MP2 energy data. Full correlated natural orbitals from a relaxed correlated one-particle density matrix are not implemented in this input and should not be inferred from the PNO summary.