QED-CI

An open-source package to simulate strongly correlated molecules coupled to quantized cavity modes.

Features

• Supports restricted references at the RHF or CQED-RHF levels, where the coherent state transformation is used for CQED-RHF
• Supports correlated levels including: QED-FCI, QED-CASCI, SA-QED-CASSCF
• Supports analytic gradients for ground- and excited- (polariton) states at the SA-QED-CASSCF level

Within the src/ directory (source-only):

• helper_cqed_rhf.py provides restricted hartree fock for the Pauli-Fierz Hamiltonian in the coherent state basis
• helper_PFCI.py provides helper functions for arbitrary CI with Pauli-Fierz Hamiltonian
• gmres.py, residual_minimization.py, ortho_script.py, and nuclear_grad.py provide supporting numerical routines

Example workflows and run scripts now live in examples/.

Getting Started

0. Clone repo

1. Install psi4

Using Conda (easy option):

• conda install psi4 python=3.10 -c conda-forge

or

From source (harder option):

• Follow directions here

2. Install numba and pytest:

• pip install numba pytest

Note other python dependencies should be installed if you used the Conda option. Other dependencies include numpy and scipy.

3. Build the native C helpers

See BUILDING.md for Linux/Intel and macOS/Apple Silicon options.

Quick examples:

• make
• make CC=icx
• make CC=clang BACKEND=accelerate

4. Run tests

• From the repository root (qed-ci/), run pytest -v tests/