My Research
Here is the link for my CV: Sharma's CV (last updated Jul-2018)
Wait! This page needs to be updated. Except for my CV, none of the information on this page is updated after 2012!
My research interests mainly cover the computational aspects of the materials science.
Major part of my thesis work comprises of understanding the structural, electronic, magnetic and optical properties of graphene and its inorganic analogues (together with their one and zero dimensional counterparts) using density functional theory (DFT) and time-dependent DFT.
Other than DFT, I have used semi-empirical methods/models like Hubbard, DFTB, ZINDO etc. I am good at shell scripting and I have written codes (along with my group members, in FORTRAN and Python) to solve the PPP model in CI space.
Apart from graphene related materials, I have also studied chlorophylls, gold clusters in ionic-liquids, perovskite oxides and metal-organic frameworks along with my experimental/theoretical collaborators.
Sharma, it is better to update your research as either presentations or google docs and embed them directly here. This way, you can easily write equations, for example, using AutoLatex, in google docs and also this will avoid documenting the things many times (documenting only one time in google docs will be sufficient!). This seems to me as a much cleaner approach even when we want to include tables, figures etc. Moreover, we can even embed a youtube videos. This is a wonderful asset because you can record your presentations and upload them here to spread your research, easily.
Own works:
By "Own works", I mean the works which I did either alone or along with my own group members
GQDs and BNQDs: Substitution
Aim of the Work:
To know the structural stability and to find the electronic, magnetic and optical properties of rectangular graphene and boron-nitride quantum dots. Effects of size, substitution and external electric-field on these quantum dots are also studied. An [arxiv version can be seen here]
Brief explanation of the Work:
The left side of the above table of contents figure of the original paper shows what are the systems we have considered and what are the external parameters we have changed (like substitution, size, electric-field). How these external parameters changed the properties of both GQDs and BNQDs are given on the right hand side of the TOC figure. Interesting properties like half-metallicity, width-dependent HOMO-LUMO gap, wide range of absorption and electric-field driven spin-polarized HOMO-LUMO gaps can be seen in the right part of the figure.
In particular, using density functional theory calculations, we have examined the structural stability, electronic, magnetic and optical properties of rectangular shaped quantum dots (QDs) of graphene (G), Boron Nitride (BN) and their hybrids. Different hybrid QDs have been considered by substituting a GQD (BNQD) with BN-pairs (carbon atoms) at different positions. Several parameters like size, amount of substitution etc. have been varied for all these QDs (GQDs, BNQDs, hybrid-QDs) to monitor the corresponding changes in their properties. Among the considered parameters, we find that substitution can act as a powerful tool to attain interesting properties with these QDs, for example, broad range of absorption (~4000 nm) in the near infrared (NIR) region, spin-polarized HOMO-LUMO gaps without the application of any external-bias etc., which are highly required in the preparation of opto-electronic, electronic/spintronic devices etc. Explanations have been given in details by varying different factors, like, changing the position and amount of substitution, application of external electric-field etc., to ensure the reliability of our results.
Acknowledgements for this work:
Many thanks to Mr. Dibya Jyothi Gosh for an early view at our manuscript. I would like to thank Ms. Arkamita Bandyopadyay for being a part of the work and also for helping me in completing this work at a faster pace. Indeed, major part of the job submission has been taken care by her. My sincere thanks to Prof. Swapan K Pati for his constant support through out this work and also for his help as well as guidance which he has given to me in achieving the present shape of the manuscript.
GQDs and BNQDs: Molecular charge transfer
Aim of the Work:
To show that molecular charge-transfer interactions can be used a simple tool to tune the electronic and optical properties of Graphene Quantum Dots (GQDs) and Boron-Nitride Quantum Dots (BNQDs). [Original paper can be seen here] and an [arxiv version can be seen here]
Brief explanation of the Work:
The above table of contents figure of the original paper shows the electronic donating nature of the TTF and electron withdrawing nature of the TCNQ from both GQD and BNQD.
In particular, spin-polarized first-principles calculations have been performed to tune the electronic and optical properties of graphene (G) and boron-nitride (BN) quantum dots (QDs) through molecular charge-transfer using Tetracyanoquinodimethane (TCNQ) and Tetrathiafulvalene (TTF) as dopants. From our calculations, we find that the nature of interaction between the dopants and QDs is similar to the interaction between the dopants and their two-dimensional counter parts of the QDs, namely, graphene and hexagonal boron-nitride sheets. Based on the values of formation energy and distance between QDs and dopants, we find that both the dopants are physisorbed on the QDs. Also, we find that GQDs interact strongly with the dopants compared to the BNQDS. Interestingly, though the dopants are physisorbed on QDs, their interaction lead to a decrement in the HOMO-LUMO gap of QDs by more than half of their original value. We have also observed a spin-polarized HOMO-LUMO gap in certain QD-dopant complexes. Mulliken population analysis, Density of states (DOS), projected DOS (pDOS) plots and optical conductivity calculations have been performed to support and understand the reasons behind the above mentioned findings.
Acknowledgements for this work:
Once again, I would like to thank Ms. Arkamita Bandyopadyay for being a part of the work. My sincere thanks to Prof. Swapan K Pati for his constant support through out this work.
BNNR: Stone-Wales defect
Aim of the Work:
To study the effects of even and odd Stone-Wales line-defects on the electronic and magnetic properties of Boron-Nitride Nanoribbons. [Original paper can be seen here] and an [arxiv version can be seen here]
Brief explanation of the Work:
The above table-of-contents figure from the original paper shows how one can easily distinguish a perfect boron-nitride nanoribbon from a boron-nitride nanoribbbon with either a one-line-defect or a two-line-defect (all the edges highlighted with green color) using simple projected-Density-of-States (pDOS) plots. When we introduce an odd-line-defect to a perfect BNNR, it will change its electronic behavior from half-metallic to semiconductor because of the change in its edge behavior from zigzag to armchair. Whereas, when an even-line-defect is introduced it will retain its half-metallicity because of the presence of the zigzag edges. Figure also shows that, an even-line-defect (if it can be created) is more helpful than an odd-line-defect in the case of a BNNR as it can lead to a robust half-metallicity (a material property which will has immense application in the field of spintronics).
Acknowledgements for this work:
I would like to thank Dr. Prakash Parida and Dr. Arun K Manna for several fruitful discussions and Prof. Swapan K Pati for his constant support through out this work.
Chlorophyll-f: Structural and Excited State Properties
Aim of the Work:
A computational study has been performed to understand the reason behind the red-shift in the absorption maximum of Chlorophyll f compared to Chlorophyll-b, where, Chlorophyll-f is a structural isomer of Chlorophyll-b. [Original paper can be seen here] and an
Brief explanation of the Work:
The above table-of-contents figure shows that the reason for the red-shift in the absorption maximum of the chlorophyll-f is mainly due to the presence of the extra conjugation (indicated by a green color circle) at the -CHO group which is present only in the Lowest Unoccupied Molecular Orbital (LUMO) of Chlorophyllide-f but not for chlorophyllide-b. Unlike the LUMO, the Highest Occupied Molecular Orbitals (HOMO) of both Chlide-f and Chlide-b have similar amount of conjugation, and also their energies are of the same order (not shown in this figure). The extra conjugation by the -CHO group stabilizes the LUMO of the Chlide-f. Now, as HOMO levels are at the same energy but the LUMO of only Chlide-f is stabilized, obviously, the gap between the HOMO and the LUMO will be less for the case of Chlide-f and more for the Chlide-b. As the wavelength is inversely proportional to the frequency (and hence, the energy), there is a red-shift in absorption maximum for the case of Chlide-f (whose HOMO-LUMO gap is less).
Apart from the above we have performed several calculations to understand how the axial ligands can effect the optical, structural properties of Chlide-f. Five different axial ligands viz., Histidine, Aspartic-acid, Water, Serine and Tyrosine have been considered. Further details of the work are given in the paper.
Acknowledgements for this work:
The idea behind this work is mainly from Dr. Ganga Periasamy and I would like to thank her for introducing me to this work. I would like to thank Prof. Swapan K Pati for his constant support through out this work.
Collobrative Works:
By Collobrative works, I mean those works which I did to support the work of the first/main author of the paper.
1. A computational study to support the findings of experimental results regarding the shifts in Raman-spectra of graphene and Carbon Nanotube samples when adsorbed by interhalogen compounds like IBr, ICl etc. [Original paper can be seen here]
2.