Time-Dependent Multicomponent Density Functional Theory for Coupled Electron-Positron Dynamics

Abstract

Electron-positron interactions have been utilized in various fields of science. Here we develop time-dependent multi-component density functional theory to study the coupled electron-positron dynamics from first principles. We prove that there are coupled time-dependent single-particle equations that can provide the electron and positron density dynamics, and derive the formally exact expression for their effective potentials. Introducing the adiabatic local density approximation to time-dependent electron-positron correlation, we apply the theory to the dynamics of a positronic lithium hydride molecule under a laser field. We demonstrate the significance of electron-positron dynamical correlation by revealing the complex positron detachment mechanism and the suppression of electronic resonant excitation by the screening effect of the positron.When a low-energy positron beam is directed to a material, the incident positron diffuses inside the bulk and is finally annihilated with atomic electrons and γ rays are emitted [1]. Analysis of these γ rays provides various information related with the surface structures, lattice defects, and electronic structures of the material [1][2][3]. The analysis of positron-annihilation γ rays has been utilized in many applications, such as positron annihilation spectroscopy [4] and positron emission tomography [5]. The positron-material interaction plays a key role in these experiments [6]. The interaction between positron and atom or molecule has also been widely studied to better understand how positrons interact with atomic electrons and are bound to them [7,8]. An experiment that measured positron-atom binding energies through the study of positron-atom recombination under a laser field was recently reported [9].Theoretical approaches to study these positron physics have been extensively developed [10]. Among them, two-component density functional theory (2C-DFT) [2,11], which is an extension of DFT [12] to the coupled electron-positron system, has been a powerful first-principles tool to calculate the ground-state electron and positron densities and their properties. 2C-DFT has been successfully applied to studies of positron interaction with atoms, solids and surfaces to determine the electron-positron momentum distributions [13], positron annihilation lifetimes [14], and positron binding energies [15], to name a few. Another powerful method is the wavefunction-based approach, such as the multi-component molecular orbital method [16] and quantum Monte Carlo method [17,18], which have also revealed much positron physics with high accuracy. However, the dynamical interaction mechanism between positrons and electrons, especially under a laser field [7-9], has not yet been clarified, because there has been no first-principles method that can simulate the correlated dynamics of positrons and electrons for realistic systems.In this study, we develop time-dependent multicomponent density functional theory (TDMCDFT) [19,20] toward an understanding of the mechanism of coupled electro...

Real-time ab initio simulation of inelastic electron scattering using the exact, density functional, and alternative approaches

“…Although a two-electron system is the extreme limit of a many-electron system, DFT or TDDFT remains effective even for this simplest case of a many-electron system, as illustrated by an example of the helium atom [33,34]. Furthermore, the exact solution of a simple 1D system, consisting of a very few electrons and atoms, has been exploited to verify nuclear quantum effects [35,36] and the ALDA [26,31,37,38] in terms of TDDFT. Hence, the 1D system consisting of an incoming electron and a stationary hydrogen atom would also permit us to validate the ALDA in treating scattering processes.…”

Current status of deMon2k for the investigation of the early stages of matter irradiation by time-dependent DFT approaches

“…Those spectra have also been computed from real-time (RT) propagation of the electronic and nuclear densities [97]. In addition, RT-TD-MC-DFT propagation has been used to study the dynamics of a positronic molecule in a laser field [98]. Furthermore, the RT-TD-MC-DFT method has been coupled with Ehrenfest dynamics to study excited-state proton transfer reactions [99].…”

Beyond Electrons: Correlation and Self-Energy in Multicomponent Density Functional Theory

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