Theoretical and computational studies of nano-structures and nanomaterials

Theoretical analysis and computer simulations have proven to be cost-effective and powerful tools in scientific studies of materials, particularly at nano-scale where synthesis of nano-structures, interpretation of their observed character and exploration of new structures are not always straightforward. We present here fundamental principles of techniques used today for computational simulations of materials, their capabilities and limitations. We then illustrate efficacy of such studies through review of their applications to nano-structures of oxide materials, carbon and boron nitride based nano-tubes and mechanical behavior of nano-structured materials. We finally present a wish-list of new tools and augmentation of existing tools that would allow expansion of the range of applications of computer simulations to nano-structures and materials

A first principles study of wurtzite-structure MnO

We present results of a density functional theory study of MnO in the wurtzite structure. Our motivation is provided by recent experiments reporting ferromagnetism in Mn-doped wurtzite structure ZnO. We find that wurtzite MnO a) is not strongly energetically disfavored as compared with the ground state rocksalt MnO, b) shows strong magnetostructural coupling and c) has a piezoelectric response that is larger than that of ZnO. These predictions augur well for the creation of ferromagnetic piezoelectric semiconductor based on Mn-doped ZnO

Anisotropy of the Stone-Wales Defect and Warping of Graphene Nano-ribbons: A First-principles Analysis

Stone-Wales (SW) defects, analogous to dislocations in crystals, play an important role in mechanical behavior of $sp^2$-bonded carbon based materials. Here, we show using first-principles calculations that a marked anisotropy in the interaction among the SW defects has interesting consequences when such defects are present near the edges of a graphene nano-ribbon: depending on their orientation with respect to edge, they result in compressive or tensile stress, and the former is responsible to depression or warping of the graphene nano-ribbon. Such warping results in delocalization of electrons in the defect states.Comment: 8 page

Localized orbital description of electronic structures of extended periodic metals, insulators, and confined systems: density functional theory calculations

We present a simple and general method for construction of localized orbitals to describe an electronic structure of extended periodic metals and insulators as well as confined systems. Spatial decay of these orbitals is found to exhibit exponential behavior for insulators and power law for metals. While these orbitals provide a clear description of bonding, they can be also used to determine polarization of insulators. Within density functional theory, we illustrate applications of this method to crystalline aluminium, copper, silicon, PbTiO3, and molecules, such as ethane and diborane