Overview
We are engaged in implementing and developing electronic structure methodologies to study several types of systems:
1. Electron transport at the molecular and nanoscale
2. Thermoelectric and photovoltaic enery conversion
3. Electron dynamics and Excited states of extended systems and biological systems.
Electron transport and transfer
A large component of our research activity pursues state of the art quantum mechanical description of electron transport. We 1) study specific molecular/nanoscale bridges and related physical phenomena and 2) develop modeling tools. Our modeling leads to unique interpretations of key experiments and provides predictions that motivate experimental advances. We acquire insight into how to control ET by chemical (i.e., metal ligation) and physical (i.e., gating field) means.
We model ET at two primary ES levels, wherein we investigate the following:
1. Molecule-based E T switching – We use density functional theory (DFT) to model the
structure-function relationships of molecular devices, and thereby highlight chemical or
physical properties that modulate the transport.
2. Dynamical ET – We use model Hamiltonians in simulating TD transport properties.
State-of-the-art computational models of molecular electronic current are based on the self consistent solution of the non-equilibrium Green's function (NEGF). We derive TD schemes as an alternative to the NEGF approach. In our approach, we used 2-variable TD expansions to gain insightful descriptions on driven and transient transport studies. These schemes utilize the TD expansions for studying transient effects in molecular devices as the system evolves to steady state and of driven transport under the influence of a laser field.
Several important applications of molecular devices are pursued.
More recently we collaborate with the Reddy group.
Other examples include the spin-dependent transmission in ligated porphyrin molecules, molecular field-effect transistors, transport in chemical sensors and studies of fundamental modeling issues. More recent studies include elaborating experimental successes in metal recognitions functionalities as recently reported by Tao and coworkers and schemes for developing molecular rectifiers.
We also model photo-induced electron-transfer processes in molecular materials relevant to PV applications. We implement and develop models based on range-separated hybrid (RSH) functionals used in the TD-DFT framework. RSH functionals have been shown to reliably treat electron transfer and delocalization. We use RSH-based models to analyze electronic emission spectra of solvated chromophores used as candidates for photovoltaic applications.
We have also study at the ES level systems that do not consider electron transfer or transport and primarily in collaboration with experimental efforts. This additional research effort studied the following:
Excited-state proton transfer, in which we examined the effects of extended electron conjugation on excited electronic states of hydrogen-bonded systems.
Reaction mechanism. For example, metal-carbide reactivity, in which we investigated the reaction mechanism and energetics of metal-carbide-containing systems at the quantum mechanical level.
Hydrogen storage, in which we studied hydrogen physisorption by organic molecules that are used in metal organic frameworks.27, 28 We also studied the hydrogen-sensing functionality of devices using the ET properties of palladium wires
Protonated aromatic system reactivity, in which we resolved the molecular fragments of the protanated systems that evolve during mass spectroscopy analysis.