Molecular Orbital Analysis of Electron Transport Through Octahedral Molybdenum Chalcogenide Clusters

The transition metal clusters are promising components of single-molecule junctions (SMJs) as they have a large number of molecular orbitals (MOs) with different symmetry and degeneracy in near-Fermi-level region, suitable for electron transmission. The chalcogenide clusters Mo₆Q₈ (Q = S, Se, Te) have high symmetry and due to the different orientations (by Mo or Q atoms to electrodes) and chalcogen variation, the transmission function (T(E)) can be tuned to achieve the desired conductive properties. In the work, the energy positions of the T(E) peaks near the Fermi level were assigned to the MOs in SMJs with Mo₆Q₈ using the nonequilibrium Green’s function formalism (NEGF) within the framework of the density functional theory. The changes of T(E) functions and MOs depending on the distances between the terminal atoms of electrodes and the embedded molecule were investigated. It is shown that for the correct assignment of MOs with T(E) peaks, it is necessary to consider long distances, even longer than those typically believed to be chemically significant. The influence of the electronic structure, symmetry of molecular orbitals, and electrodes on the SMJ transmission function was revealed. Depending on the orientation of the cluster, a different number of MOs participate in the peak of T(E) near the Fermi level, which influences the properties of the SMJs. The data obtained may be useful in the design of SMJs based on octahedral chalcogenide clusters and in tuning their conductive properties.