Executive Summary : | The generation and injection of spin-polarized current, and retention of the spin-information for a longer period of time during its transportation through conducting medium are the prerequisites for molecular spintronics applications for high-density data storage and quantum logic devices. In this context, organic semiconductors or organic-inorganic hybrid semiconductors are preferred over the traditional metal-oxide semiconductors because of the weak spin-orbit coupling in the organic molecules that enhances the spin-information retention time. However, the major challenge is to generate the spin-polarization in organic molecules. In the last two decades, several approaches have been adopted to inculcate spin-polarization such as attaching various stable magnetic subunit (i.e. radical centres) to organic molecules. The other approach was to generate transient radical species upon photochemical cleavage of the endo-peroxide bonds. The most recent approach is to induce the internal conversion of the closed-shell electronic structure to open-shell in the highly conjugated higher order polyacenes and cumulenes. In all the aforementioned cases, the spin-polarized currents were observed both theoretically as well as in various experiments. The only drawback with these approaches is that the open-shell molecules are directly involved, which are highly reactive in general. The recent photo-emission studied has discovered a completely new and sustainable approach i.e. the chiral and helical (bio-)molecules could induce similar spin-polarization. However, the exact understanding of this phenomenon is yet to be unveiled. In this proposal we will investigate various chiral molecules and helical biomolecules, especially the alpha-helix systems that take part in the electronic transportation process for the enzymatic activities in CBS-enzyme. In this proposed work we intend to adopt the density functional theory, multi-reference wavefunction theory, molecular dynamics simulations and non-equilibrium green-function based NEGF-DFT technique to compute the spin-polarized current in the chiral scattering centres. Our hypothesis is that the spin-orbital coupling at the electron-molecule interface as well as the helicity of the chiral molecules could be the controlling factors for the generation of spin-polarized currents. The major challenge in this proposal is to efficiently employ the spin-orbit coupling (SOC) included methods especially in the NEGF methodology. However, various recent developments related to ab initio electronic structure theory that includes the SOC, shade light for a successful implementation of this work. Thus the proposal is quite timely and relevant as the field is emerging and we are quite confident for a successful implementation having experience in the necessary theoretical toolbox for almost 20 years. |