Ab-initio calculations have been performed to study the geometry and electronic structure of boron (B) and nitrogen (N) doped graphene sheet. The effect of doping has been investigated by varying the concentrations of dopants from 2 % (one atom of the dopant in 50 host atoms) to 12 % (six dopant atoms in 50 atoms host atoms) and also by considering different doping sites for the same concentration of substitutional doping. All the calculations have been performed by using VASP (Vienna Ab-initio Simulation Package) based on density functional theory. By B and N doping p-type and n-type doping is induced respectively in the graphene sheet. While the planar structure of the graphene sheet remains unaffected on doping, the electronic properties change from semimetal to semiconductor with increasing number of dopants. It has been observed that isomers formed differ significantly in the stability, bond length and band gap introduced. The band gap is maximum when dopants are placed at same sublattice points of graphene due to combined effect of symmetry breaking of sub lattices and the band gap is closed when dopants are placed at adjacent positions (alternate sublattice positions). These interesting results provide the possibility of tuning the band gap of graphene as required and its application in electronic devices such as replacements to Pt based catalysts in Polymer Electrolytic Fuel Cell (PEFC).

The elastic properties of boron nitride nanotubes have been calculated using the Tersoff–Brenner potential which is a bond order potential used successfully previously for carbon nanotubes. In the present calculation, the same form of potential is used with adjusted parameters for hexagonal boron nitride. The Young’s modulus and shear modulus for single-walled armchair and zigzag tubes of different radii have been calculated. The effects of tube diameter are investigated. The computational results show the variation of Young’s modulus and shear modulus of boron nitride nanotubes with nanotube diameter. The results have been compared with available data, experimental as well as calculated.

A wide variety of nanostructure shapes have been observed for GaN under different growth conditions. These shapes include but are not limited to hexagonal pyramid, prismatic, triangular cross-section nanowires, and arrow-headed shapes. Using Wulff’s plot and kinetic Wulff’s plot for GaN under thermodynamic equilibrium and under various kinetic conditions, we present a model to theoretically predict and explain these faceted nanostructure shapes. Legendre transformation on Wulff’s plot and kinetic Wulff’s plot has been extensively utilized to obtain the faceted equilibrium shapes in equilibrium. In addition, equilibrium and nonequilibrium faceted geometry of nanostructures have also been predicted by numerical simulations using level set methods and the proposed kinetic Wulff’s plot.

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Density-functional calculations concerning the structure and stability of wurtzite AlN surfaces are presented. Specifically, (0001) and (0001¯) polar surfaces and (11¯00) and (112¯0) nonpolar surfaces are discussed in detail. Binding energies, migration pathways, and diffusion barriers for relevant adatoms such as Al, Ga, and N on these polar and nonpolar surfaces are determined. The calculation indicates low diffusion barrier for Al adatom on Al terminated (0001) surface, whereas the N adatom seems to have lower diffusion barrier on N terminated (0001¯) surfaces. A strong anisotropy was observed for diffusion behavior for Al adatom on (11¯00) and (112¯0) surfaces in the [112¯0] and [0001] directions, respectively.