Sandeep Kumar Jain

Bio: Sandeep Kumar Jain is an academic researcher from Indian Institutes of Information Technology. The author has contributed to research in topics: Ab initio & Absorption spectroscopy. The author has an hindex of 5, co-authored 12 publications receiving 62 citations. Previous affiliations of Sandeep Kumar Jain include Indian Institute of Information Technology and Management, Gwalior.

Optical properties of hexagonal boron nanotubes by first-principles calculations

Abstract: We present optical properties of hexagonal boron nanotubes (BNTs) for different schemes of incident light in the framework of density functional theory. We have considered three models of small diameter (below 5 A) BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) consisting 12, 20, and 56 atoms, respectively. In this convolution, we have investigated various optical parameters such as static dielectric constant, plasma frequency, absorption coefficient, refractive index, reflectivity, and optical conductivity for unpolarized [100], parallel polarized [001], and perpendicular polarized light [100]. The parallel and perpendicular polarized lights ensure the anisotropic nature of BNTs. The study reveals the highest static dielectric constants for chiral BNTs correspond to parallel polarized and unpolarized light, indicating good dielectric materials. The highest absorption coefficient is reported for armchair (3,3) BNT among all the considered models. Moreover, small absorption is noticed in compar...

Electron transport in asymmetric biphenyl molecular junctions: effects of conformation and molecule-electrode distance

Abstract: On the basis of ab-initio calculations, we predict the effect of conformation and molecule-electrode distance on transport properties of asymmetric molecular junctions for different electrode materials M (M = Au, Ag, Cu, and Pt). The asymmetry in these junctions is created by connecting one end of the biphenyl molecule to conjugated double thiol (model A) and single thiol (model B) groups, while the other end to Cu atom. A variety of phenomena viz. rectification, negative differential resistance (NDR), switching has been observed that can be controlled by tailoring the interface state properties through molecular conformation and molecule-electrode distance for various M. These properties are further analyzed by calculating transmission spectra, molecular orbitals, and orbital energy. It is found that Cu electrode shows significantly enhanced rectifying performance with change in torsion angles, as well as with increase in molecule-electrode distances than Au and Ag electrodes. Moreover, Pt electrode manifests distinctive multifunctional behavior combining switch, diode, and NDR. Thus, the Pt electrode is suggested to be a good potential candidate for a novel multifunctional electronic device. Our findings are compared with available experimental and theoretical results.

Optimum thickness of soft magnetic phase in FePt/FeCo permanent magnet superlattices with high energy product and large magnetic anisotropy energy

Abstract: Ab initio calculations on hard/soft (FePt)m/(FeCo)n, (m = 4, 6, 8 and n = 2-2m) magnetic superlattices show that the B2 type FeCo layers become anisotropic with varying interlayer spacing and enhanced magnetic moments. The average magnetic moment in superlattices is higher than in bulk FePt, resulting in high maximum energy product for (FePt)4/(FeCo)8 which is nearly double the calculated value for bulk FePt. The calculation of the magnetic anisotropy energy shows that the optimal thickness of the soft magnetic phase for good permanent magnet behaviour of the superlattice is less than ∼2 nm.

Structural stability of nitrogen-doped ultrathin single-walled boron nanotubes: an ab initio study

Abstract: Ab initio calculations have been performed for determining structural stabilities of nitrogen-doped ultra- thin single-walled boron nanotube. We have considered ultrathin boron nanotubes of diameters \0.5 nm, which include mainly three conformations of BNTs viz. zigzag (5,0), armchair (3,3) and chiral (4,2) with diameters 4.60, 4.78 and 4.87 A ˚ , respectively. It has been investigated that a-BNTs are highly stable, while hexagonal BNTs are found to be least stable. In view of increasing structural stability of hexagonal BNTs, substitutional doping of foreign atoms, i.e. nitrogen is chosen. The nitrogen atoms substitute the host atoms at the middle of the tubes. The substitution doping is made with all the three conformations. The structural stabilities of BNTs have been investigated by using density functional theory (DFT). Subsequently, the cohesive energy is calculated, which directly measures the structural stability. The cohesive energy of BNTs has been calculated for different nitrogen concentrations. We found that the structures get energetically more stable with increasing nitrogen concentration. Moreover, it is also revealed that all the three BNTs are almost equally stable for single-atom doping, while the armchair BNT (3,3) is highly stable followed by zigzag (5,0) and chiral (4,2) BNTs for two- and three-atom doping. The structural sta- bility is an important factor for realization of any physical device. Thus, these BNTs can be used for field emission, semiconducting and highly conducting devices at

Materials science with large-scale data and informatics: Unlocking new opportunities

Abstract: Universal access to abundant scientific data, and the software to analyze the data at scale, could fundamentally transform the field of materials science. Today, the materials community faces serious challenges to bringing about this data-accelerated research paradigm, including diversity of research areas within materials, lack of data standards, and missing incentives for sharing, among others. Nonetheless, the landscape is rapidly changing in ways that should benefit the entire materials research enterprise. We provide an overview of the current state of the materials data and informatics landscape, highlighting a few selected efforts that make more data freely available and useful to materials researchers.

Dithiocarbamate Anchoring in Molecular Wire Junctions: A First Principles Study

Abstract: Recent experimental realization [J. Am. Chem. Soc., 127 (2005) 7328] of various dithiocarbamate self assembly on gold surface opens the possibility for use of dithiocarbamate linkers to anchor molecular wires to gold electrodes. In this paper, we explore this hypothesis computationally. We computed the electron transport properties of 4,4'-bipyridine (BP), 4,4'-bipyridinium-1,1'-bis(carbodithioate) (BPBC), 4-(4'-pyridyl)-peridium-1-carbodithioate (BPC) molecule junctions based on the density functional theory and non-equilibrium Green's functions. We demonstrated that the stronger molecule-electrode coupling associated with the conjugated dithiocarbamate linker broadens transmission resonances near the Fermi energy. The broadening effect along with the extension of the $\pi$ conjugation from the molecule to the gold electrodes lead to enhanced electrical conductance for BPBC molecule. The conductance enhancement factor is as large as 25 at applied voltage bias 1.0 V. Rectification behavior is predicted for BPC molecular wire junction, which has the asymmetric anchoring groups.

Non-local exchange correlation functionals impact on the structural, electronic and optical properties of III-V arsenides

Abstract: Exchange correlation (XC) energy functionals play a vital role in the efficiency of density functional theory (DFT) calculations, more soundly in the calculation of fundamental electronic energy bandgap. In the present DFT study of III-arsenides, we investigate the implications of XC-energy functional and corresponding potential on the structural, electronic and optical properties of XAs (X = B, Al, Ga, In). Firstly we report and discuss the optimized structural lattice parameters and the band gap calculations performed within different non-local XC functionals as implemented in the DFT-packages: WIEN2k, CASTEP and SIESTA. These packages are representative of the available code in ab initio studies. We employed the LDA, GGA-PBE, GGA-WC and mBJ-LDA using WIEN2k. In CASTEP, we employed the hybrid functional, sX-LDA. Furthermore LDA, GGA-PBE and meta-GGA were employed using SIESTA code. Our results point to GGA-WC as a more appropriate approximation for the calculations of structural parameters. However our electronic bandstructure calculations at the level of mBJ-LDA potential show considerable improvements over the other XC functionals, even the sX-LDA hybrid functional. We report also the optical properties within mBJ potential, which show a nice agreement with the experimental measurements in addition to other theoretical results.

Optical properties of α-, β-, γ-, and 6,6,12-graphyne structures: First-principle calculations

Abstract: We have investigated optical properties of α -, β -, γ -, and 6,6,12-graphyne structures using first-principle calculations. In our calculations, the dielectric function, reflectivity, and absorption coefficient are calculated under both parallel and perpendicular electric field polarizations. Similar to graphene, graphynes are shown to exhibit a structure with broad frequency photoresponse. Remarkably, the results show that the optical spectra of all these graphynes are anisotropic under these two polarizations, i.e. , all these graphynes have strong reflectivity in low frequency region under the parallel polarization, but very weak reflectivity under the perpendicular polarization. Moreover, the absorption spectra of all these graphynes under the parallel polarization exhibit high values ranging from the far infrared region to the ultra-violet one. All of these features of graphynes indicate that graphynes would be good potential materials for optoelectronics.