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Vibrational frequencies of aniline in gas phase have been calculated and each of their modes of vibration assigned properly at RHF and DFT with 6-31G(d) basis set. In the present study, it has been observed that the 6-31G(d) basis set at both RHF and DFT levels of calculations provides better agreement to the experimental findings as compared to other basis sets. Simultaneously, Density functional theory is found to be superior to its counterpart Hartree Fock method.

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In this paper, we have investigated the charge stability diagram and conductance dependence on source drain bias and gate voltage of carbon nanotube based single electron transistor (SET) by using first principle calculations. All calculations have been executed by using ATK-VNL simulation package based on density functional theory (DFT). We have applied these calculations for carbon nanotube based SET; the nanotube has been placed just above the dielectric ( ) in between the source and drain electrodes of gold. The single walled carbon nanotube has been used in SET, which have ultra-small diameter and (4,0) configuration. The addition energy of the device has been calculated, which can be defined as the difference between the electron affinity, and ionization energies. The calculated values of energies have been found to be -10.17694 eV and -11.04034 eV for isolated phase and SET environment respectively. In electrostatic environment, the results were showing the regularization of molecular energy levels and therefore the addition energy reduced. The calculations for additional energies, variations of total energies to that of the gate voltages and charge stability diagram (CSD) have also been done in this study.

Low power consumption, small device size and better controlled onto the charge carriers are the factors, that made Single-electron transistor (SET) a suitable candidate for molecular electronics; yet there are some improvements that can be done in order to use it practically. The single electron transistor (SET) operates through the tunnelling of electron via two tunnel junctions. Choosing a suitable island material plays a key role in the tunnelling of electron through the tunnel junctions. In the present work, the First principle calculations of carbon-nanotube and boron-nanotube based Single-Electron Transistors have been performed. The three types of configurations of nanotubes i.e. zigzag (5,0), armchair (3,3) and chiral (4,2), of the smallest possible diameter (approximately 4A ),have been used. The calculations have been carried out using Atomistic toolkit (ATK-VNL) simulation package which is a density functional theory (DFT) based package. In the present work, local density approximations (LDA) as well as generalized gradient approximation(GGA) have been used to demonstrate the properties of nanotubes-based SET. These approaches have been implemented for a nanotube that is lying just above the gate dielectric. On the either side of the dielectric the electrodes are present, source in the left and drain in the right. The metallic electrodes made of gold (W=5.28eV) and the dielectric material of the dielectric constant have been used. The charging energies and additional energies of both types of nanotubes-based SET in the isolated as well as in the electrostatic environment have been calculated using the approximations. The calculated values of the charging energies in the electrostatic environment have been found to be less than the charging energies in isolated configuration that shows the renormalization of molecular energy levels. Variations of total energies against gate voltages and Charge stability diagrams (CSD) have been discussed.