Speaker
Description
Quantum coherence naturally arises from the many-body quantum nature of molecules. Upon strong-field ionization, a molecule can undergo a periodic oscillation of its charge density owing to coherent superposition of ionic states known as charge migration (CM) [1]. Since CM primarily arises from fundamental quantum effects such as electron correlations, it offers novel routes for probing many-body quantum coherence [2-4], chemical reactivity, photosynthesis, femto-astrochemistry and coherences in quantum science applications [1-6]. As CM is dominantly an electronic process [1-4], an appropriate theoretical treatment of the correlations is required at all levels [5-8]. The effect of molecular geometry and its electronic structure on CM has not been systematically explored. Being very crucial elements, such pathways open up novel control mechanisms to affect electronic degrees of freedom. Ultimately, control over CM could pave the way for tuning molecular response and chemical reactions by utilizing ultrashort laser pulses. However, to enable such control we first need to resolve big open questions in the field, starting with what physical mechanisms dominate CM, and especially, which determine the timescales of oscillations in the attosecond regime.
Here we perform an extensive ab initio analysis [5-8] of CM dynamics using time-dependent density functional theory (TDDFT) in a model system- BrC4H. We explore the role of electronic correlations at different levels of approximations in the CM dynamics by various exchange correlation (XC) functionals. We explore molecular attributes by artificially changing Bond Length (BL) and Bond Angle (BA) and the ionized molecular orbitals (MOs).
FIGURE 1: (I). Top: Original optimized geometry and its angular varied profiles. Bottom: MOs from which electron ionization is initiated.
(II). The hole moment evolution along the molecular backbone under various molecular attributes and levels of electronic correlations.
(III). Spectral profiles of the hole moment (from II) elucidate the presence of a universal dominant frequency beyond molecular attributes
and level of electronic correlations.
From FIGURE 1, it is evident that upon considering different levels of electronic correlations and molecular attributes, CM dynamics changes significantly in the oscillation profiles of the hole moment across the temporal scale (changing the evolution of the hole density). However, interestingly, a universal dominant frequency is seen arising in their respective spectral profiles for the average hole position and its velocity (the main frequency associated with attosecond CM). We directly reconstruct the dynamics in the cationic basis by a coherent superposition of cationic states, showing that a dominant universal frequency is retrieved in the spectral profile due to molecular dipole selection rules, akin to harmonic oscillator systems. Our results directly impact experimental observations of CM that dominantly probe the hole moments rather than the direct density evolution.
References
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