Speaker
Description
The interaction of a finite electronic system, such as a molecule or cluster, with an intense ultrafast laser pulse induces complex electronic and ionic dynamics. A key theoretical approach to studying these dynamics is to initiate the system with an instantaneous core-hole excitation, bypassing the need for direct simulation of the laser interaction. Recently, an unexpected phenomenon has been identified, termed dipole instability, where large-amplitude dipole oscillations emerge after irradiation by an ultrafast extreme ultraviolet (XUV) pulse[1,2,3]. This instability manifests as a delayed resurgence of the dipole signal, leading to additional ionization at later times. The dipole instability in TDDFT simulations at the LDA level questions whether it's a real effect or a flaw in the theory.
A key aspect of this study is examining the numerical reproducibility of dipole instability to determine its reliability and physical significance. Numerical reproducibility can be influenced by various factors, including input parameters, mathematical libraries, compilers, and numerical precision settings. Different libraries, such as FFTW and MKL, employ distinct algorithms and numerical approximations for Fourier transforms and matrix operations, introducing variations in key observables[4]. Specifically, we analyze how different compilers and libraries used in the QDD code may introduce numerical discrepancies that affect the observed dynamics. Further investigation is necessary to assess the robustness of dipole instability across different computational environments and laser field strengths, determining whether these discrepancies remain within acceptable tolerances or significantly impact the physical interpretation of results. Ensuring reproducibility across different computational environments is essential for building confidence in theoretical predictions of dipole instability phenomena. Our findings will provide insights into the reliability of numerical simulations in ultrafast electron dynamics research.
[1] P.-G. Reinhard, P.M. Dinh, D. Dundas, E. Suraud, M. Vincendon, On the stability of hole states in molecules and clusters, Eur. Phys. J. Spec. Top. 232 (2023) 2095
[2] P.-G. Reinhard, D. Dundas, P.M. Dinh, M. Vincendon, E. Suraud, Unexpected dipole instabilities in small molecules after ultrafast XUV irradiation, Phys. Rev. A 107 (2023) L020801
[3] D. Hughes, D. Dundas, P.M. Dinh, M. Vincendon, P.-G. Reinhard, E. Suraud, Dipole instability in molecules irradiated by XUV pulses, Eur. Phys. J. D 77 (2023) 177
[4] Benjamin A. Antunes, Claude Mazel, David R.C. Hill. Performance and reproducibility assessment of quantum dissipative dynamics framework: a comparative study of Fortran compilers, MKL, and FFTW. 2024. _x005F_xffff_hal-04684180v1