Dresden 2026 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 1: Optical Properties I
HL 1.8: Talk
Monday, March 9, 2026, 11:30–11:45, POT/0006
Quadrupole Transitions in Molecules from Real-Time Time-Dependent Density Function Theory — •Anvar Khujakulov1, Michele Michele Guerrini1, Carlo Andrea Rozzi1, and Caterina Cocchi2 — 1Institute for Condensed Matter Theory and Optics, 07743 Jena, Germany — 2Istituto Nanoscienze - 41125 Modena, Italy
The breakdown of the dipole approximation in tightly focused or short-wavelength laser fields is driven by spatial electric field variations, leading to significant beyond-dipole effects including quadrupole transitions and a nonlinear optical response [1]. We extend the Yabana-Bertsch implementation of real-time time-dependent density functional theory to include quadrupole transitions in the absorption cross-sections and apply the developed approach to atoms and small molecules. Our results reveal absorption peaks appearing above the linear absorption onset, a clear signature of quadrupole transitions. Critically, for molecules with appropriate symmetry, the quadrupole contribution to the absorption cross-section is maximized when a specific molecular axis aligns with the electric field gradient, analogous to the dipole case. By systematically rotating the molecular axis relative to the laser polarization vector, we calculate the orientation-dependent absorption cross-section and differentiate the contributions from dipole and quadrupole transitions. We quantitatively demonstrate that quadrupole transition is not a minor effect but a significant contributor to absorption spectra beyond the dipole approximation.
[1] C. Cocchi, et al., Phys. Rev. Lett. 112, 198303 (2014).
Keywords: Real-Time Time-Dependent Density Functional Theory; Quadrupole Transition; Photo-absorption Spectra; Nonlinear Optics