In the field of spintronics, spin is pursued as a possible carrier of information. Ab initio models of spintronic and magnetic systems need the ability to handle situations where electronic spin can freely evolve in space and time. Most conventional methods of modeling electronic dynamics, such as real-time time-dependent density functional theory (RT-TDDFT), are not flexible enough to handle the spin degrees of freedom in these spintronic candidates. To solve this problem, it is necessary to treat each electronic orbital as a linear combination of spin-up and spin-down components. This generalizes the dynamics to what is known as a two-component spinor framework. This allows the spin magnetic moment to evolve freely in time under the influence of external fields.<br/>We have investigated the effect of utilizing a two-component spinor basis on both electronic and nuclear dynamics. Though the initial results are promising, there remain several unanswered questions, such as how to properly incorporate strong magnetic fields (which can introduce severe gauge origin dependencies) and how to place the real time dynamics on the proper relativistic footing (which is the proper foundation for all magnetic phenomena). The answers to these questions will strongly dictate the utility of ab initio molecular dynamics for spintronic and magnetic systems. Here we report our investigations toward ab initio molecular dynamics that includes the proper treatment of spin interactions. In particular, we explore the challenges of introducing spin-orbit coupling to the electronic dynamics as well as the challenges associated with introducing strong magnetic fields.<br/>More specifically, we report on our recent advances towards an efficient RT-TDDFT for magnetic circular dichroism (MCD) spectroscopy. The key challenge is to incorporate a static magnetic field (of which one must be cautious of gauge-origin dependencies) in addition to circularly polarized electric fields. Furthermore, given that we wish to study magnetic molecules, it is often necessary to include spin-orbit coupling and other spin interactions (taken from relativistic Hamiltonians) in order to capture the correct physical picture. We will discuss recent advances in both of these directions, as well as several challenges to the computational prediction of MCD for large magnetic systems, looking to the future of computational spectroscopy for magnetic systems, including the powerful X-ray MCD (XMCD) spectroscopies.

Towards a real-time description of magnetic systems with applications to magnetic circular dichroism spectroscopy

251st National Meeting (2016)

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