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arXiv · 2605.08691

Post-pulse dipole instability in adiabatic TDDFT: fact or artifact?

Davood B. Dar·Dhyey Ray·Neepa T. Maitra
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Abstract

Recent real-time TDDFT calculations have reported an unexpected delayed growth of molecular dipole oscillations some time after an extreme-ultraviolet (XUV) pulse is applied. We show that numerical and analytical arguments suggest that this instability is an artifact of an incorrect non-linearity introduced by the computational approach: Propagation with an adiabatic exchange-correlation approximation within the time-dependent Kohn-Sham equations of time-dependent density functional theory (TDDFT) tends to amplify initially small and pure sinusoidal oscillations in a system. On the other hand, when this same adiabatic approximation is used within the recent response-reformulated RR-TDDFT,the instability is absent. The absorbing boundary condition plays a crucial role consistent with our argument. We demonstrate this explicitly on the N2 molecule subject to an XUV pulse, with a range of adiabatic functionals.

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Davood B. Dar, Dhyey Ray, Neepa T. Maitra. 2026-05-09. Post-pulse dipole instability in adiabatic TDDFT: fact or artifact?. https://arxiv.org/abs/2605.08691

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