Beyond the Condon limit: Condensed phase optical spectra from atomistic simulations

• DOI: 10.1063/5.0180405
• Publication Date: 2023-12-28T11:18:39Z
• Authors: Zachary R. Wiethorn; Kye E. Hunter; Tim J. Zuehlsdorff; Andrés Montoya-Ca...
• Keywords: Thermal fluctuations

While dark transitions made bright by molecular motions determine the optoelectronic properties of many materials, simulating such non-Condon effects in condensed phase spectroscopy remains a fundamental challenge. We derive Gaussian theory to predict and analyze optical spectra beyond Condon limit. Our introduces novel quantities that encode how nuclear modulate energy gap transition dipole electronic form spectral densities. By formulating through statistical framework thermal averages fluctuations, we circumvent limitations widely used microscopically harmonic theories, allowing us tackle systems with generally anharmonic atomistic interactions fluctuations arbitrary strength. show calculate these densities using first-principles simulations, capturing realistic incorporating finite-temperature, disorder, dynamical effects. accurately predicts known exhibit strong (phenolate various solvents) reveals distinct mechanisms for peak splitting: timescale separation modes tune interference from correlated fluctuations. further introduce analysis tools identify intramolecular vibrations, solute-solvent interactions, environmental polarization impact transitions. Moreover, prove an upper bound on strength cross thereby elucidating simple condition system must follow our its spectrum.