Time dependent vibrational electronic coupled cluster (VECC) theory for non-adiabatic nuclear dynamics

• Published in: The Journal of chemical physics 2024-03, Vol.160 (9)
• Main Authors: Bao, Songhao, Raymond, Neil, Nooijen, Marcel
• Format: Article
• Language: English
• Subjects: Absorption spectra; Adiabatic flow; Clusters; Electron states; Equations of motion; Mathematical analysis; Polynomials; Time dependence
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/5.0190034

A time-dependent vibrational electronic coupled-cluster (VECC) approach is proposed to simulate photo-electron/UV-VIS absorption spectra as well as time-dependent properties for non-adiabatic vibronic models, going beyond the Born–Oppenheimer approximation. A detailed derivation of the equations of motion and a motivation for the ansatz are presented. The VECC method employs second-quantized bosonic construction operators and a mixed linear and exponential ansatz to form a compact representation of the time-dependent wave-function. Importantly, the method does not require a basis set, has only a few user-defined inputs, and has a classical (polynomial) scaling with respect to the number of degrees of freedom (of the vibronic model), resulting in a favorable computational cost. In benchmark applications to small models and molecules, the VECC method provides accurate results compared to multi-configurational time-dependent Hartree calculations when predicting short-time dynamical properties (i.e., photo-electron/UV–VIS absorption spectra) for non-adiabatic vibronic models. To illustrate the capabilities, the VECC method is also successfully applied to a large vibronic model for hexahelicene with 14 electronic states and 63 normal modes, developed in the group by Aranda and Santoro [J. Chem. Theory Comput. 17, 1691, (2021)].