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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. Source


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. Source


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. Source


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. Source


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. Source

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