The Liouville-space approach offers a notationally powerful way of developing response functions in a density-based formalism and has previously been used for response theory based on exact eigenstates of the unperturbed Hamiltonian. In such density-based approaches, the fundamental units of description are pairs of quantum-mechanical states (or approximate such states), and this allows for greater descriptive power of relaxation effects (such as decoherence) without recourse to explicit statistical ensembles, compared to wavefunction-based approaches, where the units of description are not pairs of states but single such states.
In this new paper, published in the Journal of Chemical Physics, we present a Liouville-space second-quantization formulation of response theory for non-eigenstates of the unperturbed Hamiltonian in the SCF approximation, extending the theoretical framework for response theory for this category of states. This paper is firmly situated in the realm of theory development and represents the main outcome of a long-standing effort stemming from the RESHAPE project - a FRIPRO Mobility Grant project.
Date of publication: February 18, 2025.