PyQED: A Python Framework for Ab Initio Geometric Quantum Dynamics

PyQED is an open-source Python package designed for the numerical simulation of strongly coupled electron-nuclear quantum dynamics, in particular, conical intersection dynamics. Besides conventional nonadiabatic wavepacket dynamics methods based on the Born-Huang representation and mixed quantum-classical Ehrenfest dynamics, PyQED implements the geometric quantum dynamics based on the local diabatic representation, which provides a numerically exact framework for nonadiabatic quantum molecular dynamics. It differs from the conventional Born-Huang representation in that all non-Born-Oppenheimer effects are accounted for by a single electronic overlap matrix between adiabatic states, therefore removing the singular derivative couplings. The complete workflow for ab initio modeling of conical intersection dynamics is illustrated through the internal conversion dynamics in the H+3 cation. PyQED provides a powerful and user-friendly computational platform for first-principles quantum dynamics, with applications to photochemical and photophysical processes.