PyQED user guide#

The user guide organizes PyQED by scientific task. It reuses the canonical method, example, and API pages rather than repeating their content. Choose a topic below, run its smallest example first, and check the stated maturity and limitations before adapting it to a research calculation.

Important

PyQED is active research software. A module being importable does not mean every option is supported or validated. Consult the capability matrix and the limitations on the relevant method page.

New to PyQED?#

Install PyQED in an isolated environment.
Run the five-minute H2 quickstart.
Read How PyQED calculations work for the common model–build–solve–validate workflow.
Pick a task-oriented path in Tutorials and learning paths or browse the runnable examples index.

Foundations and common workflow#

How PyQED calculations work explains how inputs, numerical representations, solver objects, diagnostics, and validation fit together.
Theory overview introduces the Hamiltonian, wavefunction, density-matrix, response, and representation conventions shared across method areas.
Backends and integral representations describes native, dense, packed, RI, and factorized electronic-structure paths.
API entry points maps supported workflows to their modules; it is a navigation aid rather than a blanket stability promise.

Electronic structure#

Start with the native RHF workflow, then add correlation or response only after the reference calculation is converged.

Quantum chemistry overview – molecule construction, solver families, and integral choices.
Hartree–Fock analysis – orbitals, populations, and diagnostics after SCF.
MP2 and COMP2 – perturbative correlation workflows.
CASCI and CASSCF – active spaces, orbital optimization, state averaging, and convergence controls.
OM2/MRCI – current semiempirical excited-state interface and its validation limits.
GW and BSE and TDDFT/Ehrenfest – advanced response and excited-state paths.

Grid, quantum, and nonadiabatic dynamics#

Discrete variable representations – grid construction, kinetic energy, Hamiltonian assembly, and diagonalization.
Geometric quantum dynamics – geometric and locally diabatic representations.
Nonadiabatic dynamics API – available NAMD objects and implementation entry points.
TDDFT and Ehrenfest dynamics – coupled electronic–nuclear workflows and current backend restrictions.

Open systems and spectroscopy#

Open quantum dynamics – Lindblad, Redfield, time-convolutionless, and hierarchy-based concepts.
HEOM and structured baths – solver imports, optional dependencies, hierarchy controls, and reproducibility requirements.
Nonlinear molecular spectroscopy – sum-over-states, correlation-function, and nonperturbative viewpoints.

Light–matter and periodically driven systems#

Floquet methods – periodically driven model workflows.
Polariton methods – coupled light–matter model entry points.
Model Hamiltonians – reusable model-building components.

Tensor networks and many-body methods#

Matrix product states – MPS/MPO concepts, DMRG, package map, and example entry points.
Non-Abelian DMRG design – reduced-sector conventions and the status of spin-adapted research paths.

Reliability, reproduction, and help#

Capability maturity states which workflows are Beta or Experimental and points to their evidence.
Benchmarks and validation separates regression tests, independent validation, and performance claims.
Citing PyQED explains software, method, version, and input citation.
Support and problem reports lists the information needed for a useful scientific bug report.