Dr Vijay Kumar Foundation

Gurgaon, India

Dr Vijay Kumar Foundation

Gurgaon, India
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Manjanath A.,Indian Institute of Science | Kumar V.,Dr Vijay Kumar Foundation | Kumar V.,Shiv Nadar University | Singh A.K.,Indian Institute of Science
Physical Chemistry Chemical Physics | Year: 2014

Silicene, a graphene analogue of silicon, has been generating immense interest due to its potential for applications in miniaturized devices. Unlike planar graphene, silicene prefers a buckled structure. Here we explore the possibility of stabilizing the planar form of silicene by Ni doping using first principles density functional theory based calculations. It is found that planar as well as buckled structure is stable for Ni-doped silicene, but the buckled sheet has slightly lower total energy. The planar silicene sheet has unstable phonon modes. A comparative study of the mechanical properties reveals that the in-plane stiffness of both the pristine and the doped planar silicene is higher compared to that of the buckled silicene. This suggests that planar silicene is mechanically more robust. Electronic structure calculations of the planar and buckled Ni-doped silicene show that the energy bands at the Dirac point transform from linear behavior to parabolic dispersion. Furthermore, we extend our study to Ge and Sn sheets that are also stable and the trends of comparable mechanical stability of the planar and buckled phases remain the same.


Jaiswal S.,Dr Vijay Kumar Foundation | Jaiswal S.,SunRise University | Babar V.P.,Dr Vijay Kumar Foundation | Kumar V.,Dr Vijay Kumar Foundation | Kumar V.,Shiv Nadar University
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We report results of ab initio calculations on Y-doped anion Sin clusters with n = 4-20. Our results suggest two growth behaviors in the intermediate range of n = 8 and 20: (1) There is the formation of linked clusters in which a metal atom links two subclusters and (2) where silicon atoms form a cage structure and the metal atom is inside the cage to produce endohedral cages of silicon clusters. The cluster structures have been identified by comparing the calculated spectra of the electronic states with the photoemission spectra on anion clusters. Our results suggest that in some cases a higher energy isomer may be present in experiments. We report the calculations of the infrared and Raman spectra as well as the dipole moments, electron affinity, and polarizability that could provide other ways of identifying the growth behavior in these clusters. © 2013 American Physical Society.


Rahane A.B.,Dr Vijay Kumar Foundation | Kumar V.,Dr Vijay Kumar Foundation | Kumar V.,Shiv Nadar University
Nanoscale | Year: 2015

We report the finding of a bowl-shaped quasi-planar structure of a B84 cluster with four hexagonal holes and a three-chain ring all around the edges using ab initio calculations. A large number of other isomers including those explored earlier such as an empty cage, a filled cage, and a disordered structure, have been found to lie in a significantly higher energy band. A tubular structure, however, is only about 0.45 eV higher in energy. Calculations of the infrared and Raman spectra show that the quasi-planar structure is dynamically stable. These results suggest that quasi-planar structures may be among the low energy structures for larger clusters as well. Accordingly we have calculated the optimal quasi-planar structures stabilized with 2, 3, 5, 6, and 7 hexagonal holes also. The stability of quasi-planar structures is discussed in terms of multi-center two-electron bonding and it is shown that with increasing size their binding energy tends to approach the value for an α-boron sheet. This journal is © The Royal Society of Chemistry.


Rahane A.B.,HPT Arts and RYK Science College | Rahane A.B.,University of Pune | Deshpande M.D.,HPT Arts and RYK Science College | Kumar V.,Dr Vijay Kumar Foundation
Journal of Physical Chemistry C | Year: 2012

Atomic structures and physical properties of Gd-doped alumina clusters-namely, GdAl 2n-1O 3n and Gd 2Al 2n-2O 3n with n = 1-10-have been studied within the framework of spin-polarized density functional theory and the projector augmented wave pseudopotential method. We find that the atomic structures of the host clusters (Al 2O 3) n are not changed significantly by the substitutional doping of a Gd atom on Al sites. Our results show that in the size range of the clusters we studied, a Gd atom prefers a maximum 4-fold-coordinated Al-site, except for n = 8, in which a 5-fold-coordinated Al site is favored. The substitution of Al with Gd atom is energetically favorable. This is in contrast to the substitutional doping of Gd in the bulk alumina corundum structure that is endothermic. There is a net magnetic moment of 7 μ B per Gd atom, which is mostly localized on the Gd atom. Further substitution of an Al atom with Gd in GdAl 2n-1O 3n clusters results in the lowest-energy configuration's being either ferromagnetic or antiferromagnetic, the difference between the two magnetic states being very small. The variation in the magnetic state is found to be associated with the variation in the coordination number of Gd atoms and the sites of the two Gd atoms. Our results suggest that Gd doping of nanoparticles offers an interesting way to prepare Gd-doped ceramic materials. © 2012 American Chemical Society.


Rahane A.B.,HPT Arts and RYK Science College | Rahane A.B.,University of Pune | Deshpande M.D.,HPT Arts and RYK Science College | Kumar V.,Dr Vijay Kumar Foundation
Journal of Physical Chemistry C | Year: 2011

The atomic structures, growth behavior, and electronic properties of (Al2O3)n, n = 1-10, clusters have been studied within the framework of density functional pseudopotential theory and generalized gradient approximation for the exchange-correlation energy. The lowest energy isomers of these clusters show preference for 4-membered Al 2O2 and 6-membered Al3O3 rings. There are 3-, 4-, and 5-fold coordinated Al atoms and 2-, 3-, and 4-fold coordinated oxygen atoms. The atomic structures have similarity with that of the γ-Al2O3 phase and the average coordinations of Al and O atoms in clusters are much lower from the values in the ground state of α-Al2O3 (corundum structure). In general, isomers with cage structures lie significantly higher in energy compared with the lowest energy structures we have obtained. The bonding characteristics for clusters of different sizes is studied using Bader charge analysis. It is found that with increasing size, the charge transfer from Al atoms to oxygen increases toward the value in bulk. Further, the infrared (IR) and Raman spectra have been calculated. For n = 4, a comparison of the calculated IR spectra for a few isomers with the available experimental results on cation shows the possibility of the occurrence of a mixture of isomers in experiments. The Raman spectra of these isomers are, however, quite different. Therefore, it is suggested that measurements on Raman spectra could give a clear indication of the isomer present in experiments. © 2011 American Chemical Society.


Yadav B.D.,Dr Vijay Kumar Foundation | Yadav B.D.,University of Pune | Kumar V.,Dr Vijay Kumar Foundation
Applied Physics Letters | Year: 2010

We report from ab initio calculations a magic magnetic cage cluster of gold, Gd@ Au15, obtained by doping of a Gd atom in gold clusters. It has a highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.31 eV within the generalized gradient approximation that makes it a potential candidate for cancer therapy with an additional attractive feature that its large magnetic moment of 7 μB could be beneficial for magnetic resonance imaging. © 2010 American Institute of Physics.


Shinde P.P.,Dr Vijay Kumar Foundation | Shinde P.P.,University of Pune | Kumar V.,Dr Vijay Kumar Foundation
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Ab-initio calculations on graphene doped with boron nitride (BN) nanoribbons and patches show opening of a band gap in all cases. The smallest width of graphene in these hybrid layers controls the band gap that varies slowly around ∼0.75 eV when the width of graphene region is in the range of 2 to 5 zigzag chains. Most interestingly the band gap is direct in all the cases we have studied and nearly the same for different doping if the smallest graphene width is the same. These results show the possibility of ultrathin hybrid semiconductor graphene with band gap similar to silicon and an additional attractive feature that it is direct. © 2011 American Physical Society.


Kaur P.,Dr Vijay Kumar Foundation | Sekhon S.S.,Guru Nanak Dev University | Kumar V.,Dr Vijay Kumar Foundation
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Small nanoparticles of III-V compound semiconductors have often been considered to have open-cage structures. However, using first-principles calculations, we report the finding of a structural transition from empty-cage structures for (AlN) n and (GaN) n nanoparticles up to n = 34 that we studied, to a filled-cage structure for (InN) 32. Further, phosphides and arsenides of Al and In have an early transition to three-dimensional (3D) filled-cage structures. Our results show that a 3D (AlP) 13 is strongly magic with high binding energy and large highest occupied-lowest unoccupied molecular orbital gap. But nanoparticles of GaP show a transition from an empty cage for n = 13 to a strongly magic 3D filled cage for n = 32. The latter has a cage of (GaP) 28 and a (GaP) 4 squashed cube inside, the atoms on which are well connected with the cage. The bonding characteristics and the reason for structural transition are discussed. © 2012 American Physical Society.


Bruno Cruz A.V.,Dr Vijay Kumar Foundation | Shinde P.P.,Dr Vijay Kumar Foundation | Kumar V.,Dr Vijay Kumar Foundation | Zavada J.M.,North Carolina State University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

First principles calculations using pseudopotentials and generalized gradient approximation (GGA) for the exchange-correlation energy show that addition of Si makes Eu doping in GaN energetically favorable. It breaks local symmetry around Eu ions and leads to shallow states below the conduction band that could facilitate intra-4f shell transitions. Silicon atoms on Ga sites act as intrinsic donors transforming Eu from a 3+ to a 2+ state. The half-filled 4f states with a 7 μ B magnetic moment on each Eu ion lie within the band gap of GaN and are narrower compared with the only-Eu doping case due to reduced hybridization with the host states. There is a tendency for clustering of Eu ions with ferromagnetic coupling and the ∼5-Å interatomic distance, but EuN phase formation is unfavorable. Further effects of the inclusion of onsite Coulomb interaction U within GGA+U formalism on the electronic structure are discussed. © 2012 American Physical Society.


Shinde P.P.,Dr Vijay Kumar Foundation | Yadav B.D.,Dr Vijay Kumar Foundation | Kumar V.,Dr Vijay Kumar Foundation
Journal of Materials Science | Year: 2012

The evolution of atomic and electronic structure of small Au n (n = 1-16, and 55) clusters doped with a Gd atom has been investigated using density functional theory within generalized gradient approximation for the exchange-correlation energy. Pure gold neutral clusters with n up to 15 are planar. However, with the doping of a Gd atom, the atomic structure of gold clusters changes, and there is a transition from planar-like structures to three dimensional structures at n = 10. The electronic structure of Gd-doped gold clusters shows a sharp increase in the highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) gap for certain sizes giving rise to their magic behavior. All clusters are magnetic with large magnetic moments ranging from 6 to 8 μB primarily due to the localized 4f electrons on Gd. This makes such clusters with large HOMO-LUMO gaps magnetic superatoms. The main interaction between gold and gadolinium atoms in the clusters is due to hybridization between Au-6s and Gd-5d6s orbitals. Our results indicate the emergence of a wheel structure for Gd@Au7, a symmetric cage structure at n = 15 for Gd@Au15 and n = 16 for Gd@Au16 + and Eu@Au16 corresponding to an electronic shell closing at 18 valence electrons leaving aside the f electrons on Gd while for Gd-doped Au 55 corresponding to 58 valence electrons, a Au9Gd@Au 46 core-shell structure is obtained in which the Gd atom connects the core of Au9 with the Au46 shell. The binding energy shows odd-even oscillations with enhancement due to Gd doping compared with pure gold clusters. Such magnetic clusters of gold could have multifunctional biological applications in drug delivery, sensor, imaging, and cancer treatment. © 2012 Springer Science+Business Media, LLC.

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