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.

Electrons ransported through a chiral molecule become spin−polarized; this phenomenon is known as chiral induced spin selectivity (CISS). It has implications for spintronics, for electrochemical and enantioselective reactions, and for electron transfer in biological systems. The CISS‐induced spin polarization in simulations and in experiment differs by orders of magnitude, and the detailed underlying mechanism is still an open question. Structure−property relationships can help elucidate this question. For this purpose, the effect of helix pitch is studied for a model helix of 20 carbon atoms for two quantities which have been found to correlate in some experiments: spin‐polarization in transmitted electrons and electronic circular dichroism (ECD). We find that even though the chirality of these model helices goes down with increased pitch, ECD and CISS go up, along with ultraviolet−visible (UV/Vis) spectra and magnetic and electric transition dipole moments. Orbital contributions to the most intense UV/Vis transition do not show a consistent qualitative picture. Tentatively, we can assign the increase in these properties to an increase of the electric polarizability with spatial extension of these helices by changing pitch.

Electrons transported through a chiral molecule become spin-polarized; this phenomenon is known as chiral induced spin selectivity (CISS). It has implications for spintronics, for electrochemical and enantioselective reactions, and for electron transfer in biological systems. The CISS-induced spin polarization in simulations and in experiment differs by orders of magnitude, and the detailed underlying mechanism is still an open question. Structure-property relationships can help elucidate this question. For this purpose, the effect of helix pitch is studied for a model helix of 20 carbon atoms for two quantities that have been found to correlate in some experiments: spin-polarization in transmitted electrons and electronic circular dichroism (ECD). We find that even though the chirality of these model helices goes down with increased pitch, ECD and CISS go up, along with UV-Vis and magnetic and electric transition dipole moments. Orbital contributions to the most intense UV-Vis transition do not show a consistent qualitative picture. Tentatively, we can assign the increase in these properties to an increase of the electric polarizability with the spatial extension of these helices by changing pitch.