Modeling Ultrafast Electron Dynamics in Strong Magnetic Fields Using Real-Time Time-Dependent Electronic Structure Methods

Abstract

An implementation of real-time time-dependent Hartree–Fock (RT-TDHF) and current density functional theory (RT-TDCDFT) for molecules in strong uniform magnetic fields is presented. In contrast to earlier implementations, the present work enables the use of the RT-TDCDFT formalism, which explicitly includes field-dependent terms in the exchange–correlation functional. A range of current-dependent exchange–correlation functionals based on the TPSS functional are considered, including a range-separated variant, which is particularly suitable for application to excited state calculations. The performance of a wide range of propagator algorithms for real-time methods is investigated in this context. A recently proposed molecular orbital pair decomposition analysis allows for assignment of electronic transitions, providing detailed information about which molecular orbitals are involved in each excitation. The application of these methods is demonstrated for the electronic absorption spectra of N 2 and H 2 O both in the absence and in the presence of a magnetic field. The dependence of electronic spectra on the magnetic field strength and its orientation relative to the molecule is studied. The complex evolution of the absorption spectra with magnetic field is rationalized using the molecular orbital pair decomposition analysis, which provides crucial insight in strong fields where the spectra are radically different from their zero-field counterparts.

Optimizing Molecular Geometries in Strong Magnetic Fields

“…Interest has grown over recent years in the nonperturbative calculation of electronic structure in strong magnetic fields. − Such calculations are of interest since they are one means by which static response properties with respect to an applied magnetic field may be evaluated but also since they are essential for modeling the behavior of molecular systems in strong magnetic fields that cannot be treated perturbatively and of the kind found on stellar objects such as magnetic white dwarf stars. − Molecular hydrogen has been observed in spectra from nonmagnetic white dwarf stars, suggesting that molecules and even chemistry may be possible in such extreme environments. The behavior of carbon nanomaterials, such as nanographenes, under strong magnetic fields achievable in laboratories has long been of interest.…”

“…Initial developments and investigations concerned the application of Hartree–Fock theory to systems in strong magnetic fields, , with subsequent work employing configuration interaction, coupled-cluster theory, equation of motion coupled-cluster theory, , current–density functional theory, , and most recently the calculation of spectra using real-time time-dependent self-consistent field methods. − , Several electronic structure packages have been developed or generalized to treat systems in strong magnetic fields, starting with the London quantum chemistry program and followed by the Bagel program, the ChronusQ package, Turbomole , and our own development code Quest…”

“…Initial developments and investigations concerned the application of Hartree−Fock theory to systems in strong magnetic fields, 1,2 with subsequent work employing configuration interaction, 24 coupled-cluster theory, 9 equation of motion coupled-cluster theory, 10,11 current−density functional theory, 12,13 and most recently the calculation of spectra using real-time time-dependent self-consistent field methods. [6][7][8]17 Several electronic structure packages have been developed or generalized to treat systems in strong magnetic fields, starting with the LONDON quantum chemistry program 24 and followed by the BAGEL program, 25 the CHRONUSQ package, 26 TURBOMOLE, 27 and our own development code QUEST. 28 Central to these developments has been the use of Gaussiantype London atomic orbitals (LAOs), 29 which comprise a standard Gaussian basis function multiplied with a complex plane-wave phase factor dependent on the external magnetic field and the gauge origin.…”

The GW/BSE Method in Magnetic Fields

“…The description of excited states of molecules in strong magnetic fields poses a major challenge for quantum chemical methods. ( Delos et al, 1983 ; Turbiner and López Vieyra, 2004 ; Hampe and Stopkowicz, 2017 ; Stopkowicz, 2018 ; Hampe and Stopkowicz, 2019 ; Wibowo et al, 2021 ). On the one hand, it is well known that introducing magnetic fields also introduces a gauge-dependence when standard, real-valued Gaussian-type basis functions are used.…”

“…Even though the computational limitations are severe, the investigation of molecular properties in strong external magnetic fields has become an increasingly popular topic within the field of quantum chemistry in recent years. Several field-dependent properties including non-linear effects on the electronic structure of small molecules, ( Tellgren et al, 2008 ; Tellgren et al, 2009 ; Lange et al, 2012 ; Stopkowicz et al, 2015 ), molecular geometries, ( Tellgren et al, 2012 ; Irons et al, 2021 ), spin-phase transitions ( Sun et al, 2019a ) and excited state properties ( Sun et al, 2019b ; Sen et al, 2019 ; Stetina et al, 2019 ; Wibowo et al, 2021 ) have been explored using quantum-chemical methods at different levels of theory.…”