Electron Correlation in Real Time

Abstract

Electron correlation, caused by the interaction among electrons in a multielectron system, manifests itself in all states of matter. A complete theoretical description of interacting electrons is challenging; different approximations have been developed to describe the fundamental aspects of the correlation that drives the evolution of simple (few-electron systems in atoms/molecules) as well as complex (multielectron wave functions in atoms, molecules, and solids) systems. Electron correlation plays a key role in the relaxation mechanisms that characterize excited states of neutral or ionized atoms and molecules populated by absorption of extreme ultraviolet (XUV) or X-ray radiation. The dynamics of these states can lead to different processes such as Fano resonance and Auger decay in atoms or interatomic Coulombic decay or charge migration in molecules and clusters. Many of these relaxation mechanisms are ubiquitous in nature and characterize the interaction of complex systems, such as biomolecules, adsorbates on surfaces, and hydrogen-bonded clusters, with XUV light. These mechanisms evolve typically on the femtosecond (1 fs=10(-15) s) or sub-femtosecond timescale. The experimental availability of few-femtosecond and attosecond (1 as=10(-18) s) XUV pulses achieved in the last 10 years offers, for the first time, the opportunity to excite and probe in time these dynamics giving the possibility to trace and control multielectron processes. The generation of ultrashort XUV radiation has triggered the development and application of spectroscopy techniques that can achieve time resolution well into the attosecond domain, thereby offering information on the correlated electronic motion and on the correlation between electron and nuclear motion. A deeper understanding of how electron correlation works could have a large impact in several research fields, such as biochemistry and biology, and trigger important developments in the design and optimization of electronic devices.

Electronic reorganization triggered by electron transfer: The intervalence charge transfer of a Fe3+/Fe2+ bimetallic complex

“…The energetic cost of the IVCT excitation without any cooperation of the electronic‐sphere (0%), the so‐called rigid electron transfer, is 12.57 eV. The rigid IVCT is in a sense equivalent to a Koopmans' ion state, the theoretical final state of an ultrafast ionization . This state is obtained by removing one electron from one orbital of the neutral species without taking into account the adaptation of other electrons (i.e., excluding electron correlation), following the prescription of Koopmans' theorem .…”

Unified theory of quantized electrons, phonons, and photons out of equilibrium: A simplifiedab initioapproach based on the generalized Baym-Kadanoff ansatz

“…while the expectation value of the vector potential  satisfies the equation of motion (2). (38) The ⊥ superscript means that only the transverse part of the current enters in the Eq.…”

“…Using the same procedure as above we can evaluate a similar derivative δ n(1) δN ext (2) . In this case, the interaction with N ext is d 3 rV n (r)N ext (r,t).…”

Some exact properties of the nonequilibrium response function for transient photoabsorption

“…By recording the photoemission or photoabsorption spectrum produced by a second, weak pulse, hereafter named probe, impacting the sample with a tunable delay from the pump a large variety of ultrafast physical and chemical processes can be documented. [1][2][3][4][5][6] Time-resolved pump-and-probe (P&P) spectroscopies have revealed the formation and dynamics of excitons, [7][8][9][10][11] charge-transfer excitations, [12][13][14][15][16][17][18][19][20] autoionized states 21,22 and light-dressed states, [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] the evolution of Fano resonances, [38][39][40][41][42][43] the screening build-up of charged excitations, [44][45][46][47] the transient transpa...…”