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Physics@VCU Links:
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Research Interests
Dr. Shiv N. Khanna
Professor
Chemical Physics
Figure: Valence density for the isolated Mn12 O12 atoms shows that there is covalent bonding between the O and Mn atoms. See Pederson and Khanna, PRB 59 R693 (1999).
With recent developments in materials science, it is now possible to fabricate new
materials whose size, dimensionality, and composition can be controlled. This
includes: free clusters of atoms containing 2 to a few thousand atoms; quasicrystalline
materials having periodicity prohibited by conventional solid state physics; layers
and multilayer materials; and nanostructured particles. These systems are showing novel
electronic, magnetic, thermodynamic, chemical and optical properties. Our research
here is geared towards a theoretical study of these novel materials.
A major effort of work is directed towards the electronic structure, geometry
and the magnetism of clusters. The theoretical schemes used range from
first-principles density functional methods capable of describing clusters having up to 20
atoms to
tight-binding and semi-empirical techniques capable of describing clusters having
several hundred atoms. We have already studied neutral and charged clusters of several
elements and have provided information on their geometries and electronic structure.
Our current work is focusing on metallo-carbohedrenes, a 20-atom cluster containing
transition metal atoms and C-atoms that has been recently discovered. This new class
of clusters are variants of the C60 buckyballs and are expected to have applications in
magnetic storage devices, catalysts, pollution control and biological systems. We are
investigating how these are formed, how they grow, and how their properties can be
modified by adding foreign atoms.
In addition to clusters, a good part of our effort is directed towards magnetic super
lattices. It is now possible to grow layered materials involving layers of two elements.
These layered materials exhibit a coupling between layers which can change as the
thickness of the spacer layer is changed. We are theoretically investigating the
magnetic properties of these layered materials.
Another area currently being investigated concerns the MnAl quasicrystal discovered
in 1984. These alloys exhibit a local icosahedric symmetry prohibited by conventional
crystallography, and the question is how does the new symmetry affect the electronic
and magnetic behavior. We are investigating the magnetic moment of a Mn atom and
the electronic structure of these systems.
In addition to the above problems, we are looking at the melting of small clusters, ways
of inducing magnetism in non-magnetic solids, and designing new cluster-solids where
each site would be a clusters.
Publications with Nanostructured Materials Consortium
 Physics Homepage.
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