arXiv subjects

Eberhard K. U. Gross

Publications and source records attributed to Eberhard K. U. Gross.

6 recordsLinked to original sources

arXiv2017

Understanding Band Gaps of Solids in Generalized Kohn-Sham Theory

The fundamental energy gap of a periodic solid distinguishes insulators from metals and characterizes low-energy single-electron excitations. But the gap in the band-structure of the exact multiplicative Kohn-Sham (KS) potential substantially underestimates the fundamental gap, a major limitation of KS density functional theory. Here we give a simple proof of a new theorem: In generalized KS theory (GKS), the band gap of an extended system equals the fundamental gap for the approximate functional if the GKS potential operator is continuous and the density change is delocalized when an electron or hole is added. Our theorem explains how GKS band gaps from meta-generalized gradient approximations (meta-GGAs) and hybrid functionals can be more realistic than those from GGAs or even from the exact KS potential. The theorem also follows from earlier work. The band edges in the GKS one-electron spectrum are also related to measurable energies. A linear chain of hydrogen molecules, solid aluminum arsenide, and solid argon provide numerical illustrations.

cond-mat.mtrl-sci↗

arXiv2016

Swift thermal steering of domain walls in ferromagnetic MnBi stripes

We predict a fast domain wall (DW) motion induced by a thermal gradient across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an exchange torque fueled by magnon accumulation at the DWs. Depending on the thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions are possible. The finding unveils an energy efficient way to manipulate DWs as an essential element in magnetic information processing such as racetrack memory.

cond-mat.mtrl-sci↗

arXiv2014

Local measurement of the Eliashberg function of Pb islands: enhancement of electron-phonon coupling by quantum well states

Inelastic tunneling spectroscopy of Pb islands on Cu(111) obtained by scanning tunneling microscopy below 1K provides a direct access to the local Eliashberg function of the islands with high energy resolution. The Eliashberg function describes the electron-phonon interaction causing conventional superconductivity. The measured Eliashberg function strongly depends on the local thickness of the Pb nanostructures and shows a sharp maximum when quantum well states of the Pb islands come close to the Fermi energy. Ab initio calculations reveal that this is related to enhanced electron-phonon coupling at these thicknesses.

cond-mat.supr-con↗

arXiv2010

Controlling the Dynamics of Many-Electron Systems from First Principles: A Marriage of Optimal Control and Time-Dependent Density-Functional Theory

Quantum Optimal Control Theory (QOCT) provides the necessary tools to theoretically design driving fields capable of controlling a quantum system towards a given state or along a prescribed path in Hilbert space. This theory must be complemented with a suitable model for describing the dynamics of the quantum system. Here, we are concerned with many electron systems (atoms, molecules, quantum dots, etc) irradiated with laser pulses. The full solution of the many electron Schr{ö}dinger equation is not feasible in general, and therefore, if we aim to an ab initio description, a suitable choice is time-dependent density-functional theory (TDDFT). In this work, we establish the equations that combine TDDFT with QOCT, and demonstrate their numerical feasibility with examples.

physics.atm-clus↗

arXiv2006

An exact Coulomb cutoff technique for supercell calculations

We present a new reciprocal space analytical method to cutoff the long range interactions in supercell calculations for systems that are infinite and periodic in 1 or 2 dimensions, extending previous works for finite systems. The proposed cutoffs are functions in Fourier space, that are used as a multiplicative factor to screen the bare Coulomb interaction. The functions are analytic everywhere but in a sub-domain of the Fourier space that depends on the periodic dimensionality. We show that the divergences that lead to the non-analytical behaviour can be exactly cancelled when both the ionic and the Hartree potential are properly screened. This technique is exact, fast, and very easy to implement in already existing supercell codes. To illustrate the performance of the new scheme, we apply it to the case of the Coulomb interaction in systems with reduced periodicity (as one-dimensional chains and layers). For those test cases we address the impact of the cutoff in different relevant quantities for ground and excited state properties, namely: the convergence of the ground state properties, the static polarisability of the system, the quasiparticle corrections in the GW scheme and in the binding energy of the excitonic states in the Bethe-Salpeter equation. The results are very promising.

cond-mat.other↗

arXiv2005

Time-dependent electron localization function

In this article we present a generalization of the electron localization function (ELF) that can be used to analyze time-dependent processes. The time-dependent ELF allows the time-resolved observation of the formation, the modulation, and the breaking of chemical bonds, and can thus provide a visual understanding of complex reactions involving the dynamics of excited electrons. We illustrate the usefulness of the time-dependent ELF by two examples: the pi-pi* transition induced by a laser field, and the destruction of bonds and formation of lone pairs in a scattering process.

physics.chem-ph↗