Chiral-Induced Spin Selectivity and Non-equilibrium Spin Accumulation in Molecules and Interfaces: A First-Principles Study

Electrons moving through chiral molecules are selected
according
to their spin orientation and the helicity of the molecule, an effect
known as chiral-induced spin selectivity (CISS). The underlying physical
mechanism is not yet completely understood. To help elucidate this
mechanism, a non-equilibrium Green’s function method, combined
with a Landauer approach and density functional theory, is applied
to carbon helices contacted by gold electrodes, resulting in spin
polarization of transmitted electrons. Spin polarization is also observed
in the non-equilibrium electronic structure of the junctions. While
this spin polarization is small, its sign changes with the direction
of the current and with the handedness of the molecule. While these
calculations were performed with a pure exchange-correlation functional,
previous studies suggest that computationally more expensive hybrid
functionals may lead to considerably larger spin polarization in the
electronic structure. Thus, non-equilibrium spin polarization could
be a key component in understanding the CISS mechanism.