libwfa: Wavefunction analysis tools for excited and open‐shell electronic states

Abstract

An open-source software library for wavefunction analysis, libwfa, provides a comprehensive and flexible toolbox for post-processing excited-state calculations, featuring a hierarchy of interconnected visual and quantitative analysis methods. These tools afford compact graphical representations of various excited-state processes, provide detailed insight into electronic structure, and are suitable for automated processing of large data sets. The analysis is based on reduced quantities, such as state and transition density matrices (DMs), and allows one to distill simple molecular orbital pictures of physical phenomena from intricate correlated wavefunctions. The implemented descriptors provide a rigorous link between many-body wavefunctions and intuitive physical and chemical models, for example, exciton binding, double excitations, orbital relaxation, and polyradical character. A broad range of quantum-chemical methods is interfaced with libwfa via a uniform interface layer in the form of DMs. This contribution reviews the structure of libwfa and highlights its capabilities by several representative use cases.

Providing theoretical insight into the role of symmetry in the photoisomerization mechanism of a non-symmetric dithienylethene photoswitch

“…Additionaly, we performed a wavefunction analysis to provide information on the character of the S 0 → S 1 and S 0 → S 2 transitions. The analysis is based on the squared norm ( Ω ) of the one-particle transition density matrix (1TDM) 74 between the ground state and the S 1 and S 2 excited states, the NTO participation ratio (PR NTO ) and the number of entangled states ( Z HE ). 75 It must be mentioned that Ω is a universal measure of single-excitation character and PR NTO and Z HE provide inherent information on the multiconfigurational character of the transition.…”

Using diketopyrrolopyrroles to stabilize double excitation and control internal conversion

“…Turning now to the contribution of the building blocks to the doubly excited character, we analyze the 2A g state in more detail using systematic wavefunction analysis techniques. We focus on three main descriptors: Ω , 68 which accounts for the amount of singly excited configurations; 68 the number of unpaired electrons 53 ( n u,nl ); and the promotion number 55 ( p ), which indicates the number of electrons promoted in the photoexcitations. 55 Ω is obtained from the one-particle transition density matrix (1TDM) between the ground and excited state, n u,nl is computed from the excited-state density matrix, and p is computed from the difference density matrix.…”

Using diketopyrrolopyrroles to stabilize double excitation and control internal conversion

“…Turning now to the contribution of the building blocks to the doubly excited character, we analyze the 2Ag state in more detail using systematic wavefunction analysis techniques. We focus on three main descriptors:  49 which accounts for the amount of singly excited configurations 49 ; the number of unpaired electrons 39 (nu,nl); and the promotion number 41 (p), which indicates the number of electrons promoted in the photoexcitations. 41  is obtained from the one-particle transition density matrix (1TDM) between the ground and excited state, nu,nl is computed from the excited-state density matrix, and p is computed from the difference density matrix.…”