arXiv subjects

Kondayya Gundra

Publications and source records attributed to Kondayya Gundra.

3 recordsLinked to original sources

arXiv2011

A Fortran 90 Hartree-Fock program for one-dimensional periodic $π$-conjugated systems using Pariser-Parr-Pople model

Pariser-Parr-Pople (P-P-P) model Hamiltonian is employed frequently to study the electronic structure and optical properties of $π$-conjugated systems. In this paper we describe a Fortran 90 computer program which uses the P-P-P model Hamiltonian to solve the Hartree-Fock (HF) equation for infinitely long, one-dimensional, periodic, $π$-electron systems. The code is capable of computing the band structure, as also the linear optical absorption spectrum, by using the tight-binding (TB) and the HF methods. Furthermore, using our program the user can solve the HF equation in the presence of a finite external electric field, thereby, allowing the simulation of gated systems. We apply our code to compute various properties of polymers such as $trans$-polyacetylene ($t$-PA), poly-\emph{para}-phenylene (PPP), and armchair and zigzag graphene nanoribbons, in the infinite length limit.

physics.comp-ph↗

arXiv2011

Band Structure and Optical Absorption in Multilayer Armchair Graphene Nanoribbons: A Pariser-Parr-Pople Model Study

Using the tight binding and Pariser-Parr-Pople (PPP) model Hamiltonians, we study the electronic structure and optical response of multilayer armchair graphene nanoribbons (AGNRs), both with and without a gate bias. In particular, the influence of the number of layers ($n$), and the strength of the electric field applied perpendicular to layers, for different types of edge alignments, is explored on their electro-optical properties. As a function of increasing $n$, the energy gap initially decreases, eventually saturating for large $n$. The intensity of the linear optical absorption in these systems also increases with increasing $n$, and depends crucially on the polarization direction of the incident light, and the type of the edge alignment. This provides an efficient way of determining the nature of the edge alignment, and $n$, in the experiments. In the presence of a gate bias, the intensity of optical absorption behaves in a nontrivial way. The absorption becomes more intense for the large fields in narrow ribbons exhibiting a red shift of the band gap with the increasing field strength, while in broad ribbons exhibiting a blue shift, the absorption becomes weaker. However, for smaller electric fields, the absorption intensity exhibits more complicated behavior with respect to the field strength. Thus, the effect of the gate bias on optical absorption intensity in multilayer AGNRs is in sharp contrast to the bilayer graphene, which exhibits only enhancement of the absorption intensity with the increasing electric field.

cond-mat.mtrl-sci↗

arXiv2011

Theory of Electro-Optical Properties of Graphene Nanoribbons

We present calculations of the optical absorption and electro-absorption spectra of graphene nanoribbons (GNRs) using a $π-$electron approach, incorporating long-range Coulomb interactions within the Pariser-Parr-Pople (PPP) model Hamiltonian. The approach is carefully bench marked by computing quantities such as the band structure, electric-field driven half metallicity, and linear optical absorption spectra of GNRs of various types, and the results are in good agreement with those obtained using\emph{ab initio} calculations. Our predictions on the linear absorption spectra for the transversely polarized photons provide a means to characterize GNRs by optical probes. We also compute the electro-absorption spectra of the zigzag GNRs, and argue that it can be used to determine, whether or not, they have a magnetic ground state, thereby allowing the edge magnetism to be probed through non-magnetic experiments.

cond-mat.mtrl-sci↗