Speaker- Yosuke Kanai, Department of Chemistry

Title: Ab Initio Simulation of Thouless Pumping of Electrons in Floquet Topological Phase

I will discuss nonadiabatic Thouless pumping of electrons in trans-polyacetylene and related systems in the framework of topological Floquet engineering using first-principles theory.  By employing maximally localized Wannier function gauge in real-time time-dependent density functional theory, we connect the winding number, a topological invariant, to a molecular-level understanding of the quantized pumping via valence bond model. Exploiting the gauge-invariant nature of the quantum dynamics with respect to single-particle orbitals, we show that so-called dynamical transition orbitals give a minimal description of the dynamics in terms of the particle-hole excitation. The quantum dynamics responsible for the Thouless pumping is largely characterized by the dynamics of a single orbital as it undergoes changes from its π bonding orbital character at equilibrium to acquiring resonance and antibonding characters in the driving cycle. This allows us to explain the presence/absence of the Floquet topological phase in the polymer systems with seemingly minor chemical changes on the basis of the valence bond model. I will conclude by discussing existing challenges in first-principles theory for modeling electron dynamics in increasingly complex systems and phenomena.