Abstract:
Many interesting and counter intuitive properties have been predicted over decades in low-dimensional
systems. i.e. systems. confined to less than three dimensions. In this thesis, we have investigated the
electronic structure and optical properties of a few low-dimensional systeM.S. viz., graphene, graphene
nanoribbons, single-walled carbon nanotubes and chlorophylls.
In chapter 1, we gave a brief introduction to low-dimensional systeM.S. and we have mentioned
some exotic properties of all the low-dimensional systeM.S. which we investigated in this thesis. In this
chapter we also introduced the computational and theoretical methods like DFT, TDDFT etc. which we
have used to determine the electronic structure and optical properties of the materials.
In chapter 2, we applied density functional theory (DFT) to understand the interaction of
halogen/ interhalogen molecules with nanocarbons (graphene and carbon nanotubes). Previous
experimental studies on halogen-nanocarbon composites show a charge transfer from nanocarbon to
halogens and correspondingly a shift in the Raman G-band of nanocarbons. In our study, we find shifts
in the Fermi-level of nanocarbons up on the adsorption of halogen/ interhalogen molecules. Our
findings shows that shift in the Fermi-level and the Raman G-band are in accordance with each other
and the amount of shift in Fermi-level or Raman G-band depends on the electron affinity character of
halogen/ interhalogen molecules.
In chapter 3, we investigated the effect of axial ligation on the structural, redox and absorption
properties of a newly discovered chlorophyll, named chl f, and explained the reasons for the observed
changes. We have also given the reason for the red-shift in the Qy band of chl f compared to other chls,
like chl a and chl b, based on the time dependent density functional theory studies.
Chapter 4 is the final chapter and it is a presentation of work in progress. In this chapter, we
studied the structural dependency of the nonlinear optical (NLO) properties of graphene nanoribbons
(GNRs). In particular, we considered zigzag GNRs (ZGNRs) of various sizes, both in length and
width, and studied the variation in linear and hyper-polarizability by changing the size of ZGNRs. We
find that hyper-polarizability value of ZGNRs increases with an increase in the conjugation and the
values are large enough to use ZGNRs as donor-acceptor bridges. Calculations of polarizability and
hyper-polarizability of ZGNRs attached with different donors and acceptors are in progress.
