Kavita Joshi

Kavita Joshi

Physical and Materials Chemistry Division

About Me

We do electronic structure calculations to understand, predict, and design new materials.

Professional Experience

  • 2014 --       Sr. Scientist, NCL, Pune
  • 2010 -- 13  Scientist Fellow, NCL, Pune, India
  • 2005 -- 09  Research Associate, University of Pune, Pune , India.
  • 2004 -- 05  Postdoctoral Fellow at CEA-Grenoble France.

Selected Publications

  • A. Susan, V. Kaware And K. Joshi*, Multifaceted Thermodynamics of Pbn (n=16-24) Clusters: A Case Study, J. Phys. Chem. C., 119, 23698 - 23707 (2015), DOI:10.1021/acs.jpcc.5b05250.
    Thermodynamic response of small clusters is a challenging area of exploration, both experimentally, as well as theoretically. In this article, we study the thermodynamic behaviour of small Pb clusters (size 16--24) using Born Oppenheimer Molecular Dynamics. A new ground state structure is reported for Pb$_{20}$. Except Pb$_{21}$, all clusters fragment at temperatures above T$_{m[bulk]}$, and show no signs of melting. Characteristic behaviour like restricted diffusion and solid-solid transition is discussed in detail. Variation in the isomerization temperature of these clusters is explained using the bondlength analysis. Root mean square bondlength fluctuations (\deltarms) along with distribution of atoms about centre of mass of the cluster as a function of time and distance-energy plots are used to bring out the essential features of Pb cluster thermodynamics. Analysis carried out using these parameters, and their interpretation regarding state of the system, are discussed in detail. We highlight that it is not possible to define `liquid-state' for these small clusters, in the conventional frame of understanding.
  • Vaibhav Kaware and Kavita Joshi*, Scaling up the shape: A novel growth pattern of gallium clusters, J. Chem. Phys., 141, 054308 (2014), DOI:http://dx.doi.org/10.1063/1.4891867.
    Putative global minima for Ga+N clusters with size “N” ranging from 49 to 70 are found by employing the Kohn-Sham formulation of the density functional theory, and their evolution is described and discussed in detail. We have discovered a unique growth pattern in these clusters, all of which are hollow core-shell structures. They evolve with size from one spherical core-shell to the next spherical core-shell structure mediated by prolate geometries, with an increase in overall diameter of the core, as well as the shell, without putting on new layers of atoms. We also present a complete picture of bonding in gallium clusters by critically analyzing the molecular orbitals, the electron localization function, and Bader charges. Bonding in these clusters is a mixture of metallic and covalent type that leans towards covalency, accompanied by marginal charge transfer from the surface to the core. Most molecular orbitals of Ga clusters are non-jellium type. Covalency of bonding is supported by a wide localization window of electron localization function, and joining of its basins along the bonds.
  • A. Susan, A. Kibey, V. Kaware And K. Joshi*, Correlation between the variation in observed melting temperatures and structural motifs of the global minima of gallium clusters: An ab initio study, Journal of Chemical Physics., 138, 014303 (2013), DOI:http://dx.doi.org/10.1063/1.4772470.
    We have investigated the correlation between the variation in the melting temperature and the growth pattern of small positively charged gallium clusters. Significant shift in the melting temperatures was observed for a change of only few atoms in the size of the cluster. Clusters with size between 31?42 atoms melt between 500–600 K whereas those with 46?48 atoms melt around 800 K. Density functional theory based first principles simulations have been carried out on Ga+n clusters with n = 31,?…, 48. At least 150 geometry optimizations have been performed towards the search for the global minima for each size resulting in about 3000 geometry optimizations. For gallium clusters in this size range, the emergence of spherical structures as the ground state leads to higher melting temperature. The well-separated core and surface shells in these clusters delay isomerization, which results in the enhanced stability of these clusters at elevated temperatures. The observed variation in the melting temperature of these clusters therefore has a structural origin.
  • Kavita Joshi, Sailaja Krishnamurty And D. G. Kanhere, “Magic Melters” Have Geometrical Origin, Phys. Rev. Lett., 96, 135703 (2006), DOI:http://dx.doi.org/10.1103/PhysRevLett.96.135703.
    Recent experimental reports bring out extreme size sensitivity in the heat capacities of gallium and aluminum clusters. In the present work we report results of our extensive ab initio molecular dynamical simulations on Ga30 and Ga31, the pair which has shown rather dramatic size sensitivity. We trace the origin of this size sensitive heat capacities to the relative order in their respective ground state geometries. Such an effect of nature of the ground state on the characteristics of heat capacity is also seen in case of small gallium and sodium clusters, indicating that the observed size sensitivity is a generic feature of small clusters.
  • S. Chacko, Kavita Joshi, D. G. Kanhere And S. A. Blundell, Why Do Gallium Clusters Have a Higher Melting Point than the Bulk?, Phys. Rev. Lett., 92, 135506 (2004), DOI:http://dx.doi.org/10.1103/PhysRevLett.92.135506.
    Density functional molecular dynamical simulations have been performed on Ga17 and Ga13 clusters to understand the recently observed higher-than-bulk melting temperatures in small gallium clusters [G.?A. Breaux et al., Phys. Rev. Lett. 91, 215508 (2003)]. The specific-heat curve, calculated with the multiple-histogram technique, shows the melting temperature to be well above the bulk melting point of 303 K, viz., around 650 and 1400 K for Ga17 and Ga13, respectively. The higher-than-bulk melting temperatures are attributed mainly to the covalent bonding in these clusters, in contrast with the covalent-metallic bonding in the bulk.

Research Interest

  • Materials Chemistry including Nanomaterials
  • Theory AND Computational Science
  • Materials and Materials Engineering
  • Surface Science
  • Heterogeneous Catalysis
  • Nanoscience & Technology
  • Nanocatalysis

Contact Details

Kavita Joshi

Office: Ground Floor, DIRC Building
National Chemical Laboratory
Dr. Homi Bhabha Road
Pune 411008, India
Phone   +91 20 2590 2476
E-mail k.joshi@ncl.res.in