Theoretical Research

Studies on doped and undoped semiconductor nanoclusters:

Size quantization effects observed in small semiconductor clusters are currently of great interest for potential optical and other applications. We have performed first principles calculations geared towards mapping out the energy-level structures, explaining the optical absorption spectra and the response properties, as a function of size of the III-V semiconductor nanoclusters. Our aim is to search for finding doped or undoped semiconductor clusters with high non-linear optical polarizabilities, which may have potential to be used as devices.

Studies on interaction of various important molecules with semiconductor nanostructures:

Effort towards sucking up of the hazardous greenhouse gases from the air has recently gained tremendous momentum. It is expected that the carbon nanotubes and cages may adsorb these gases because of their increased surface area leading to increased absorptive capacity. Using First Principles calculations based on density functional theory, we accurately estimate the strength of the long-range van der Waals interaction, in terms of the C6 coefficients between these small greenhouse gas molecules and carbon nanostructure systems (CNS). We also compare these C6 values as a function of shape and size of the CNS. From our studies, large interactions are expected between the carbon nanotubes and greenhouse gases. Carbon nanotubes functionalized with biological molecules (such as proteins and nucleic acids) show great potential for applications in bioengineering and nanobiotechnology. Studies of interaction of amino acids with carbon nanostructures are presently being carried out.

Studies on doped and undoped semiconductor nanotubes and nanowires:

First Principles all-electron calculations based on density functional theory have been carried out to study the geometrical and electronic structures of semiconductor nanotubes. The results on electronic structures of the single-walled carbon nanotubes with ultrasmall diameters stress on the need for complete geometry optimization; and also the all-electron calculations seem to be the method of choice, specifically for the nanotubes with very small diameters. Though successful synthesis of several III-V semiconductor nanotubes have been reported in the literature, theoretical study, specifically at the first principles level, is rather scarce. A thorough geometry optimization of single walled nanotubes of Gallium Phosphide (SWGaPNT) shows that these tubes are not perfect tubes but the hexagons on the surface are buckled: Ga atoms go in and P atoms go out of the surface. The energy band structure for SWGaPNT(n,0), for n=10, reveals a semiconductor nature of these tubes, band gap of about 1.4 eV.  Probing of half metallicity and ferromagnetism following doping of these nanotubes with transition metal atoms is presently being carried out.