vibe-qc

A quantum-chemistry code for molecules and solids, with the cyclic cluster model as the long-term target.

vibe-qc is a Python + C++17 electronic-structure code built on libint (Gaussian integrals), libxc (500+ XC functionals), and spglib (crystal symmetry). The molecular feature set — Hartree-Fock, density functional theory, and second-order Møller-Plesset theory — is validated against PySCF to machine precision. The periodic feature set is currently growing toward CRYSTAL-style crystalline orbital HF and KS-DFT across 1D / 2D / 3D lattices.

At a glance

from vibeqc import Atom, Molecule, BasisSet, run_rhf

mol = Molecule([
    Atom(8, [0.0,  0.0,  0.0]),
    Atom(1, [0.0,  1.43, -0.98]),
    Atom(1, [0.0, -1.43, -0.98]),
])
basis = BasisSet(mol, "pob-tzvp")
result = run_rhf(mol, basis)
print(result.energy)      # −76.0493914670

import numpy as np
from vibeqc import PeriodicSystem, BasisSet, monkhorst_pack, run_rks_periodic
from vibeqc import PeriodicKSOptions

# 1D H2 chain
sysp = PeriodicSystem(
    dim=1,
    lattice=np.diag([4.0, 30.0, 30.0]),   # 1D axis in bohr; vacuum in y, z
    unit_cell=[Atom(1, [0,0,0]), Atom(1, [0,0,1.4])],
)
basis = BasisSet(sysp.unit_cell_molecule(), "pob-tzvp")
kmesh = monkhorst_pack(sysp, [4, 1, 1])

opts = PeriodicKSOptions()
opts.functional = "PBE"
result = run_rks_periodic(sysp, basis, kmesh, opts)
print(result.energy)

Where to go next

Getting started

• Installation
  • Requirements
  • macOS
  • Linux — Debian / Ubuntu
  • Linux — Fedora / RHEL-family
  • Linux — Conda / Mamba (any distro)
  • What each step does
  • Verifying
  • Common issues
  • Updating
• Running vibe-qc — a tour
  • 0. The simple way: run_job
  • 1. Load a molecule
  • 2. Hartree-Fock energy
  • 3. Density Functional Theory (DFT)
  • 4. ASE Calculator — the easy path
  • 5. Logging the SCF
  • 6. Geometry optimization + visualisation
  • 7. Custom basis sets
  • 8. Accessing the full API
  • 9. Running the tests
• Tutorial
  • Molecular Hartree-Fock
  • Molecular DFT (RKS)
  • Open-shell systems (UHF, UKS, UMP2)
  • Post-SCF properties: charges, bonds, dipole
  • Geometry optimisation
  • Vibrational frequencies (via ASE)
  • Thermodynamics at temperature
  • Orbital and density visualisation
  • Basis-set convergence
  • Periodic HF on a 1D H chain
  • Periodic KS-DFT
  • Madelung constants via Ewald summation
  • Band structure and density of states

User guide

• User guide
  • Molecules
  • Basis sets
  • Functionals
  • Periodic systems
  • k-point meshes
  • Ewald summation in periodic systems
  • SCF convergence
  • Memory budget
  • ASE integration
  • Input scripts and output files
  • Post-SCF properties
  • Band structure and density of states
  • Volumetric data: cube and XSF files

Reference

• Python API reference
• Feature matrix
• Roadmap

Project

• Changelog
• Contributing to vibe-qc
• License

Status

vibe-qc is pre-release software. The molecular HF/DFT/MP2 stack is stable and validated against PySCF; the periodic stack is being actively built and validated phase by phase. Follow the roadmap for what’s next.

Licensed under the Mozilla Public License 2.0.