Understanding the behavior of electrons, which includes the electronic structure as well as the dynamical response of electrons to internal and external fields in different materials is a substaintial problem in modern physics. We expect to use this understanding to design new materials and devices with specific properties.
By means of our plane-wave DFT calculations along with STM experiments, we have recently discovered a new type of electronic states of C60. Because they have spherical harmonic shapes of s, p, d, etc. atomic orbitals, and are centered on the hollow core of nearly spherical C60 molecules, we dubbed them the superatom molecular orbitals (SAMO). The hybridization of SAMOs into extended states can impart nearly free electron (NFE) transport properties to molecular materials.
We investigate the origin of the SAMOs and the factors that influence their energy and wave function hybridization into NFE bands in molecular solids. We show that the SAMOs are derived from the universal image potential states of molecular sheets by rolling and wrapping them into 0D fullerenes. We conclude that SAMOs are a general property of hollow molecules as well as nanotubes. The NFE states provide a completely different and more efficient pathway for electron transport.
The more interesting part is the dynamics of electrons at interface. On TiO2 surface, the electron dynamics has essential relationship with photocatalysis. We have studied the solvated electrons on TiO2/aqueous interface. Solvated electrons are the most fundamental chemical reagents as well as carriers of negative charge in neat liquids. At H2O/TiO2 interface, the solvated or wet electron states shows a 2D diffuse character. Based on a time-resolved two-photon photoemission (2PP) and DFT study of H2O/TiO2(110) rutile surface, the solvated electron states are found to represent the lowest energy pathway for electron transfer at the metal-oxide/aqueous interfaces and may play an important role in photocatalysis and photoelectrochemical energy conversion on TiO2 and other metal oxides. In order to study the electron dynamics of the excited wet electron, we used time-resolved 2PP to study the simplest organic molecule CH3OH on TiO2 surfaces. A pronounced deuterium isotope effect (CH3OD) was found in the solvation process. Using the Δ-SCF method based on DFT, the excited electron redistribution process can be simulated in a molecular-level. And it was found the isotope effect is corresponding to the proton couple electron transfer (PCET). The correlated motion of protons in response of the excess charge is likely to be an integral aspect of photocatalytic reactions on protic-solvent-covered metal oxide surfaces. 2PP studies along with DFT calculations on model systems provide for the first time a molecular-level view of the photophysical and photochemical process that drive photocatalysis.