AICCM quickstart¶

Two ways to run an experimental ab-initio Cyclic Cluster Model calculation: Γ-CCM (aiccm2026dev-a, union-and-weight/Wigner–Seitz integral weighting) and χ-CCM[1] (aiccm2026dev-b, finite-translation-group characters). These are distinct approaches compared at a declared common exchange-q=0 convention.

Γ-CCM / aiccm2026dev-a (union and weights)¶

cd aiccm-2026
python run_case.py h-chain aiccm-hf

Expected output (<system>__aiccm-hf.json):

{"system": "h-chain", "route": "aiccm-hf", "nrep": [8,1,1],
 "energy": -1.116713, "energy_per_atom": -0.558357, "converged": true}

Or from Python:

import numpy as np
from vibeqc import Atom, PeriodicSystem
from vibeqc.periodic.ccm import CCMSystem
from vibeqc.periodic.ccm.scf import run_ccm_rhf

BOHR = 1.0 / 0.529177210903
unit = PeriodicSystem(1, np.diag([4*BOHR, 40, 40]),
                      [Atom(1, [0,0,0]), Atom(1, [2*BOHR,0,0])])
ccm = CCMSystem(unit, (8,1,1), "sto-3g")
rhf = run_ccm_rhf(ccm, method="aiccm2026dev-a")
print(f"Γ-CCM RHF E/atom = {rhf.energy_per_atom:.6f} Ha")

χ-CCM / aiccm2026dev-b (finite-character Γ-centred character mesh)¶

cd aiccm-2026
python run_case_b.py c-diamond rhf-ri --mesh 1 1 1

The result JSON records the exact construction identity alongside the energy:

{"system": "c-diamond", "route": "rhf-ri", "mesh": [1,1,1],
 "converged": true,
 "finite_torus_convention": {
   "ccm_approach": "chi-ccm",
   "ccm_construction": "finite-translation-group-character",
   "evaluation_representation": "gamma-centred-character-mesh",
   "coulomb_kernel": "3d-periodic-g0",
   "exchange_q0": "bvk-ewald"}}

The actual JSON also carries the computed energy and full producer fingerprint.

Or from Python:

import numpy as np
import vibeqc as vq

system = vq.PeriodicSystem(3, np.diag([8, 20, 20]),
                           [vq.Atom(1, [0,0,0]), vq.Atom(1, [1.4,0,0])],
                           multiplicity=1)
basis = vq.BasisSet(system.unit_cell_molecule(), "sto-3g")
r = vq.run_periodic_job(system, basis, method="RHF",
                        jk_method="aiccm2026dev-b",
                        aiccm_lattice_extension=(1,1,1),
                        aiccm_backend="ri",
                        max_iter=40, progress=False,
                        citations=False, write_xyz_file=False,
                        output_qvf=False)
print(f"χ-CCM RHF/RI E/cell = {r.energy:.8f} Ha")

χ-CCM-B absolute-energy execution is currently 3D only. Every 1D/2D backend fails closed pending one shared wire/slab Coulomb convention.

What next?¶

you want to…	go here
Walk through step by step	Γ-CCM tutorial
See every route and backend	Γ-CCM reference or χ-CCM guide
Run open-shell	Open-shell AICCM
Debug a problem	Troubleshooting
Run the full 28-system benchmark	AICCM-2026 benchmark