Influence of Electronic Structure Modeling and Junction Structure on First-Principles Chiral Induced Spin Selectivity

Abstract

We have carried out a comprehensive study of the influence of electronic structure modeling and junction structure description on the first-principles calculation of the spin polarization in molecular junctions caused by the chiral induced spin selectivity (CISS) effect. We explore the limits and the sensitivity to modeling decisions of a Landauer/Green's function/two-component density functional theory approach to CISS. We find that although the CISS effect is entirely attributed in the literature to molecular spin filtering, spin−orbit coupling being partially inherited from the metal electrodes plays an important role in our calculations on ideal carbon helices, even though this effect cannot explain the experimental conductance results. Its magnitude depends considerably on the shape, size, and material of the metal clusters modeling the electrodes. Also, a pronounced dependence on the specific description of exchange interaction and spin−orbit coupling is manifest in our approach. This is important because the interplay between exchange effects and spin−orbit coupling may play an important role in the description of the junction magnetic response. Our calculations are relevant for the whole field of spinpolarized electron transport and electron transfer, because there is still an open discussion in the literature about the detailed underlying mechanism and the magnitude of physical parameters that need to be included to achieve a consistent description of the CISS effect: seemingly good quantitative agreement between simulation and the experiment can be caused by error compensation, because spin polarization as contained in a Landauer/Green's function/two-component density functional theory approach depends strongly on computational and structural parameters.

Theory of Chirality Induced Spin Selectivity: Progress and Challenges

“…[48,49] Recent first principles calculations for a chiral monolayer on a magnetic substrate provided first indications of an emergent electronic structure and emphasized the role of exchange interactions. [106] However, the emergent structure is generally expected and practically confirmed [34,107,108] to be sensitive to the choice of density functional and this effect was not investigated. In addition, chiral symmetry breaking was enforced "manually" via introduction of an external Ni atom, so that the effect of the intrinsic chirality remains to be clarified.…”

Chiral Perovskite Spin-Optoelectronics and Spintronics: Toward Judicious Design and Application

“…In particular, it was found that the anisotropy factor of responsivity that describes the distinguishability to CPL is reported to be much larger than g abs , which could also be attributed to the CISS effect in chiral materials. The theoretical study of the CISS effect has also not been reported in a chiral perovskite yet, but theoretical models in other chiral systems for understanding the CISS effect have been reported. − Among them, the nonequilibrium Green’s function (NEGF) technique with a model Hamiltonian is widely used to understand the spin-polarized transport; the results in double-stranded DNA, single-stranded DNA, and α-helical protein are in excellent agreement with experimental results. , …”

On the definition of chirality and enantioselective fields

“…A source of third terminal is, therefore, being looked for by several theoretical researchers. In order to overcome these problems, recent experiments and calculations suggest an involvement of phonons as a source of effective spin polarization [30][31][32][33] whereas others will try to include exchange interactions [34,35]. A model proposed here is another way to address this issue by explicitly including pseudo Jahn Teller effect into the system to include dynamics of chiral order parameter 𝐺𝐺 0 (object).…”