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

  • Shweta Mehta, Sheena Agarwal And Kavita Joshi, Catching the essence of Hohenberg-Kohn's first theorem while recreating PES for clusters with machine learning, arXiv., , (2018), DOI:https://arxiv.org/abs/1812.04932.
    To date, density functional theory (DFT) is one of the most accurate and yet practical theory to gain atomistic insight about materials properties. Although successful, the computational cost of it is the main hurdle even today. In recent years, there have been a few attempts of combining DFT with machine learning (ML) to curtail the computational cost without compromising accuracy. However, the success of this approach depends critically on the choice of the descriptors. In this letter, we demonstrate that, based on {\it only} interatomic distances as descriptors, our ML model predicts interaction energy between an adsorbate and a cluster. We have employed this model to compute the potential energy surface experienced by a test charge in the vicinity of a cluster with absolute mean error (AME) ? 0.04 eV at minimal computational cost. Our extensive DFT calculations provides the rationale of achieving improved accuracy and a proof of concept that our ML model picks up the essence of Hohenberg-Kohn's first theorem.
  • Nivedita Kenge, Sameer Pitale And Kavita Joshi, The Nature of Electrophilic Oxygen : Insights from Periodic Density Functional Theory Investigations, Surface Science., , (2018), DOI:https://doi.org/10.1016/j.susc.2018.09.009.
    Increasing demand of ethylene oxide and the cost of versatile chemical ethene has been a driving force for understanding mechanism of epoxidation to develop highly selective catalytic process. Direct epoxidation is a proposed mechanism which in theory provides 100% selectivity. A key aspect of this mechanism is an electrophilic oxygen (Oele) species forming on the Ag surface. In the past two and half decades, large number of theoretical and experimental investigations have tried to elucidate formation of Oele on Ag surface with little success. Equipped with this rich literature on Ag-O interactions, we investigate the same using periodic DFT calculations to further understand how silver surface and oxygen interact with each other from a chemical standpoint. Based on energetics, Löwdin charges, topologies and pdos data described in this study, we scrutinize the established notions of Oele. Our study provides no evidence in support of Oele being an atomic species nor a diatomic molecular species. In fact, a triatomic molecular species described in this work bears multiple signatures which are very convincing evidence for considering it as the most sought for electrophilic entity.
  • 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