This is a brief overview of our main ongoing research projects. We are grateful to our sponsors for their support.

 

Oxide surfaces

We are interested in adsorption on hematite () surfaces, and reactions taking place on those surfaces. For example, methyl free radical (•) is an important reaction intermediate which is being studied in collaboration with Peter Stair's group. Faced with the structural and chemical complexity of oxide surface, we must use a variety of theoretical tools, including:

  • MD/MC atomistic simulation to study relaxation/reconstruction
  • DFT Band Structures to examine clean surface stable structure
  • DFT Embedded Clusters to study local chemical phenomena

Functional macromolecules

The area of functional nanoscale porous molecular materials is still at an early formative stage. Recently, novel classes of cavity-containing materials assembled from discrete building blocks, dubbed as "molecular boxes", were synthesized, which offer possibilities for selective molecular separation and control over chemical processes like catalysis and sensing.

As a part of Northwestern's NIRT effort on "Molecular Squares", we are using interactively the first-principles DF and the molecular dynamics approaches in analysis of porphyrin-based boxes, to gain insight on their mechanical conformation and stability, and electronic response to their chemical environment. This work is done in collaboration with Randy Snurr's group, Joe Hupp's group, and SonBinh Nguyen's group.

Bioceramics

Bioceramics involves both natural hard tissues like tooth and bone, as well as artificial materials used in implants and prostheses. In recent years, increasing attention is being paid to physical and chemical microstructure as a way both to understand structure/function relations as well as to design improved materials. Our group has focused on the apatite structure as the ‘hydrogen atom’ of bone and tooth- hydroxyapatite Ca10(PO4)6(OH)2 can be considered as the parent of a wide range of substituted and nonstoichiometric compounds.

In collaboration with the groups of Alexandre Rossi and John Ketterson, we are studying the properties of carefully prepared/controlled-structure nanoparticles and thin films. We are particularly interested in uptake and retention of metals by the apatite lattice- transition metals such as Zn and Fe which play an important part of animal metabolism, and Pb which is a common and dangerous environmental contaminant. Applications to catalysis and waste-water remediation are being studied with our experimental collaborators at NU and in Brazil.

Conductance at interfaces

The race to produce ever smaller and faster electronic devices, while maintaining reliability and manufacturing control, has led many groups to consider electronic conductivity at the nanoscale. Density Functional theory has proved an excellent approach to treating ground state properties, thus describing chemical bonding and lattice stability at ‘zero temperature’. Understanding and controlling conductivity at elevated temperature in the presence of chemical gradients is a greater challenge, which requires development of new tools.

Several groups have explored the use of Green’s functions to describe single-molecule or nanowire conductivity, with promising results. Starting from ground state zero-voltage wavefunctions, we can try to bootstrap to self-consistent solutions of the electronic density under steady state conducting conditions. We take our starting point from the localized-orbital approach developed in Ratner’s group and are developing a similar approach to the more general interface-conductance problem.

 

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