THEORETICAL STUDY OF SOME LOW-DIMENSIONAL SYSTEMS

Abstract

The rapid expansion of nanotechnology resulting from important research efforts in a wide range of disciplines has led to a real technological breakthrough. Much work is presently focused on the study of low-dimensional systems. Among these, nanowires (NWs) are especially attractive due to their extensive use as magnetic NWs in recording. These can also be a promising candidate for electrical conduction in the integrated nanoscale systems, to connect metal nanoparticles and can also operate as sensors. Monolayers (MLs), a two dimensional system, are also having wide range of applications in thin film solid electrolytes, gas sensors, thin film transistors and thin layer electronic devices. The major challenge for nanoscience is to assemble these objects to make a stable material and, consequently, to make new devices for future technology, since silicon technology is soon going to reach the limit of miniaturization. At low dimensions where size of materials reaches the limit of nanometers, at least along one direction, behavior of the systems becomes very unconventional. Here theory and simulation play an important role in the development of real technology. The ab-initio techniques for calculations are coming widely into picture as they can provide fairly accurate description of electronic structure of materials. The domain of application for ab-initio methods is also becoming wider due to increasing power of computers. But developments are not sufficient to cover all the needs, in particular when the number of atoms in the systems becomes very large or when the system itself is very large. In this context, density functional theory (DFT) has the advantage of leading to a set of well-defined one-particle equations, much simpler to solve than Hartree-Fock ii equations, and to provide, at the same time, accurate prediction of the ground state properties. This approach, where different contributions to the electronic energy can be written as a functional of electron charge density, has been used for the calculations presented in this thesis. The exchange and correlations are dealt with under generalized gradient approximation which is a popular approximation for predicting magnetic ground state of transition metal systems. In this work, a theoretical effort has been made to investigate low-dimensional systems of transition metals. For this, the early transition metals have been chosen since nanosystems of these metals have not received as much attention theoretically as the nanosystems of the late transition metals.