QUANTArhei: Open Quantum System Theory for Molecular Systems
Quantarhei is a molecular open quantum systems simulator written in Python. Its name is derived from the aphorism "Panta rhei" of Heraclitus of Ephesus — "Everything flows" — fitting for a package centred on quantum dynamics.
It provides tools for building molecular aggregates, computing linear and non-linear spectra, and simulating excitation energy transfer and open quantum system dynamics.
Installation
From PyPI (recommended):
pip install quantarhei
With uv:
uv add quantarhei
From source:
git clone https://github.com/tmancal74/quantarhei.git
cd quantarhei
pip install -e .
Requirements: Python 3.10 or later, NumPy, SciPy.
Quick start
import quantarhei as qr
# Define two molecules with transition energies (in 1/cm)
with qr.energy_units("1/cm"):
mol1 = qr.Molecule([0.0, 12000.0])
mol2 = qr.Molecule([0.0, 12200.0])
mol1.set_dipole(0, 1, [1.0, 0.0, 0.0])
mol2.set_dipole(0, 1, [0.0, 1.0, 0.0])
# Build a dimer aggregate with resonance coupling
agg = qr.Aggregate([mol1, mol2])
with qr.energy_units("1/cm"):
agg.set_resonance_coupling(0, 1, 100.0)
agg.build()
# Calculate absorption spectrum
with qr.energy_units("1/cm"):
time = qr.TimeAxis(0.0, 1000, 1.0)
calc = qr.AbsSpectrumCalculator(time, system=agg)
spec = calc.calculate()
spec.plot()
More examples are in the docs/examples/ directory and on Read the Docs.
Features
- Molecular aggregates — multi-molecule systems with arbitrary couplings, vibrational modes (Huang-Rhys factors, intra-molecular modes), vibronic coupling, and system-bath interactions
- Linear spectroscopy — absorption, circular dichroism, linear dichroism, and fluorescence spectra for monomers and aggregates
- 2D electronic spectroscopy — non-linear response with Liouville pathway analysis, Feynman diagrams, and pump-probe spectra
- Energy transfer theories — Redfield, modified Redfield, and Förster rate theories; time-dependent and non-equilibrium variants; mixed Redfield-Förster
- Open quantum system dynamics — Lindblad and Redfield master equations, density matrix propagation, hierarchical equations of motion (HEOM)
- Bath modeling — correlation functions, spectral densities, lineshape functions; pre-built models for photosynthetic pigments
- Laboratory frame — realistic optical geometries and pulse field configurations via
LabSetup - Extensible — pure Python reference implementation; performance-critical routines can be replaced with optimised C/Fortran extensions
Interactive notebooks
Try Quantarhei in your browser — no installation needed:
| Notebook | Topic | Launch |
|---|---|---|
| Molecule & Hamiltonian | Creating molecules, energy levels, vibrational modes |  |
| Correlation Functions | Bath correlation functions C(t) and spectral density J(ω) | |
| Absorption Spectrum | Full workflow: molecule → aggregate → bath → absorption | |
| Redfield Relaxation | Density matrix propagation and population dynamics | |
| HEOM Dynamics | Strong-coupling dynamics beyond Redfield | |
Documentation
Full API reference and tutorials: quantarhei.readthedocs.io
Changelog
See CHANGELOG.md for the full version history.
Acknowledgements
The development of Quantarhei has been supported by:
- Neuron Fund for Support of Science — Impuls grant in physics 2014 (2015–2017)
- Czech Science Foundation (GACR) — grants 14-25752S (2014–2016), 17-22160S (2017–2019), 18-18022S (2018–2020)
1 maintainer
Metadata
1 maintainer
Release files for quantarhei 0.0.70
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