Role of proton quantum effects on the electronic excited states of hydrogen-bonded organic materials

Optical and optoelectronic responses of organic molecules—both in solution and as molecular crystals—are central to many technological and spectroscopic applications. Such responses are often modeled with time-dependent density functional theory, but the charge-transfer nature of the responsible electronic transitions in some organic materials makes it difficult to study them using standard exchange-correlation approximations. On the other hand, optical excitations in these organic systems sometimes trigger proton transfer processes, requiring us to consider the quantum nature of protons. In this work, we employ our new Bethe-Salpeter equation (BSE) in the quasi-particle description via BSE@GW method (1) with the nuclear electronic orbital (NEO) method (2,3) in order to examine the interplay between the electronic excitation and the proton transfer processes. We discuss the role of nuclear quantum effects in the excited states and their implication for spectroscopic measurements.

(1) All-electron BSE@GW Method with Numeric Atom-centered Orbitals for Extended Periodic Systems. R. Zhou, Y. Yao, V. Blum, X. Ren, Y. Kanai. J. Chem. Theory. Comput. 21, 291 (2025)



(2) Constrained nuclear-electronic orbital method for periodic density functional theory: Application to H₂ chemisorption on Si(001) surfaces. S. Liu, J. Xu, Y. Kanai. J. Chem. Phys. 163, 084110 (2025) - Annabella Selloni Festschrift



(3) Nuclear-Electronic Orbital Approach to Quantization of Protons in Periodic Electronic Structure Calculations. J.Xu, R. Zhou, Z. Tao, C. Malbon, V. Blum, S. Hammes-Schiffer, Y. Kanai. J. Chem. Phys. 156, 224111 (2022)