  The physical origin of the so-called chirality-induced spin selectivity
(CISS) effect has puzzled experimental and theoretical researchers over the
past few years. Early experiments were interpreted in terms of unconventional
spin-orbit interactions mediated by the helical geometry. However, more recent
experimental studies have clearly revealed that electronic exchange
interactions also play a key role in the magnetic response of chiral molecules
in singlet states. In this investigation, we use spin-polarized closed shell
density functional theory calculations to address the influence of exchange
contributions to the interaction between helical molecules as well as of
helical molecules with magnetized substrates. We show that exchange effects
result in differences in the interaction properties with magnetized surfaces,
shedding light into the possible origin of two recent important experimental
results: enantiomer separation and magnetic exchange force microscopy with AFM
tips functionalized with helical peptides.
