Towards a Merger of Nonadiabatic Molecular Dynamics and Spintronics

Joseph Subotnik of The University of Pennsylvania is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to study how electronic spin affects nuclear relaxation and can shape energy loss via heat production. In particular, Subotnik will develop new and powerful algorithms that quantify exactly how molecules with nuclei and spins relax after they have been excited by light.

Subotnik will test both theoretically and computationally which atoms move during relaxation, and will explore the possibility that this atomic motion can lead to a promotion of spin-selectivity for long periods of time. All of the algorithmic developments will be released to the public in an open source fashion. This research program lies at the cutting edge of physical chemistry and spin-chemistry, and in the long term, research here has the potential to help create an entirely new form of device electronics based on electronic spin (so-called spintronics) unlike conventional devices based on electronic charge.

The broader impacts include the Subotnik group's support for bringing undergraduate researchers into the lab, with a special emphasis on introducing members of underrepresented groups to hands-on science. The Subotnik research team also invites these students to participate the annual Penn Conference in Theoretical Chemistry (PCTC).

Subotnik will develop a semi-classical algorithm for quantifying how coupled nuclear-electronic systems prepared out of equilibrium relax in the presence of spin-orbit coupling. In the presence of spin-orbit coupling, the electronic Hamiltonian becomes complex-valued and the nature of electronic transitions becomes very difficult for modern algorithms because (i) the direction of momentum rescaling becomes unclear and (ii) the presence of Berry magnetic forces can lead to novel reaction pathways.

Subotnik is constructing and benchmarking a novel, reliable surface hopping approach to treat such conditions, both for the case of doublets (with two electronic states) as well as for the case of singlet-triplet crossings (with four electronic states). Furthermore, Subotnik will run simulations on reasonably small test cases to investigate whether the presence coupled nuclear-electronic dynamics effects (including Berry forces) may underlie recent experiments displaying a chiral induced spin selectivity (CISS) effect.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.