Year: 2026
Type: preprint
Abstract: Oscillatory real-time integrals and the complete quadratic transformation between electronic-state normal modes are persistent obstacles in molecular internal-conversion calculations. We develop a finite-temperature Tyablikov–Moskalenko Green-function formulation that retains unequal frequencies, equilibrium displacement, Duschinsky rotation, the anomalous squeezing block, and a general first-order Herzberg–Teller nonadiabatic operator. The closed equations of motion reconstruct the vibronic correlation function by coupling-constant integration, while analytic continuation to complex time permits both a systematic saddle expansion and globally controlled integration on Lefschetz thimbles without numerical damping. For the 102-mode tetraoxa[8]circulene (4B) model at 300 K, the complete rate is 1.656× 10 7 s −1 at 18500 cm −1 . Herzberg–Teller coupling and Duschinsky rotation increase the rate by factors of approximately 2.45 and 2.06, respectively, while the squeezing contribution is about 46% in the mode-mixed calculation. The next-to-leading saddle result differs from the full thimble value by 0.66% at the molecular gap; one contributing thimble and no Stokes transition are found throughout 5000–35000 cm −1 . The same formalism gives aligned electric-and magnetic-field thresholds of 1.06 × 108 V m −1 and 41.6 T. The method therefore provides a fast, damping-free route to complete harmonic vibronic rates together with an explicit global test of the integration contour.
Source: ChemRxiv
Author: Rashid Valiev
Institution: University of Helsinki
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7220950094