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

  • 2019 --      Principal Scientist
  • 2014 -- 19  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

  • Shankar B Dalavi, Sheena Agarwal, Pooja Deshpande, Kavita Joshi* And Bhagavatula L. V. Prasad*, Disordered but Efficient: Understanding the Role of Structure and Composition of the Co–Pt Alloy on the Electrocatalytic Methanol Oxidation Reaction, J. Phys. Chem. C., , (2021), DOI:https://doi.org/10.1021/acs.jpcc.0c10165.
    A systematic investigation of the electrocatalytic Methanol Oxidation Reaction (MOR) was carried out using a model Co:Pt alloy system with different compositions and structural arrangements of the Co and Pt atoms. The structural variations with the same alloy composition included those with disordered arrangement of Co and Pt atoms in a face-centered cubic (fcc) lattice and ordered arrangements in face-centered tetragonal (fct) lattices. Our investigations clearly show that structures with disordered arrangements with Co:Pt atomic ratios near to 1:1 display better electrocatalytic efficiencies even when compared to pure Pt. These experimental findings were then rationalized by means of Density Functional Theory (DFT) calculations. Electronic level signatures in terms of charge transfer and relative shift in the peaks of the d band for surface metal atoms are proposed to be the reasons for the superior catalytic activity of a particular composition over the others. An increase in the number of inequivalent sites for methanol adsorption in disordered systems appears to result in better catalytic performance in comparison with ordered systems.
  • Sheena Agarwal, Shweta Mehta And Kavita Joshi*, Understanding the ML black box with simple descriptors to predict cluster–adsorbate interaction energy, New Journal of Chemistry., 44, 8545 - 8553 (2020), DOI:10.1039/D0NJ00633E.
    Density functional theory (DFT) is currently one of the most accurate and yet practical theories used to gain insight into the properties of materials. Although successful, the computational cost required is still the main hurdle even today. In recent years, there has been a trend of combining DFT with Machine Learning (ML) to reduce the computational cost without compromising accuracy. Finding the right set of descriptors that are simple to understand in terms of giving insights about the problem at hand, lies at the heart of any ML problem. In this work, we demonstrate the use of nearest neighbor (NN) distances as descriptors to predict the interaction energy between the cluster and an adsorbate. The model is trained over a size range of 5 to 75 atom clusters. When the training and testing is carried out on mutually exclusive cluster sizes, the mean absolute error (MAE) in predicting the interaction energy is ? 0.24 eV. MAE reduces to 0.1 eV when testing and training sets include information from the complete range. Furthermore, when the same set of descriptors are tested over individual sizes, the MAE further reduces to ?0.05 eV. We bring out the correlation between dispersion in the nearest neighbor distances and variation in MAE for individual sizes. Our detailed and extensive DFT calculations provide a rationale as to why nearest neighbor distances work so well. Finally, we also demonstrate the transferability of the ML model by applying the same recipe of descriptors to systems of different elements like (Na10), bimetallic systems (Al6Ga6, Li4Sn6, and Au40Cu40) and also different adsorbates (N2, O2, and CO).
  • Pravin K. Dwivedi, Aathira Nair, Rupali S. Mehare, Vikash Chaturvedi, Kavita Joshi* And Manjusha V. Shelke*, Experimental and theoretical investigations of the effect of hetero-atom doped Carbon micro-sphere support on stability and storage capacity of nano-Co3O4 conversion anode for Lithium-ion batteries, Nanoscale Advances., 2, 2914 - 2924 (2020), DOI:10.1039/D0NA00261E.
    Conversion type anode materials are intensely being studied for Li-ion batteries (LIBs) for their potentially higher capacities over current graphite-based anodes. This work describes the development of high capacity and stable anode from a nanocomposite of N and S co-doped Carbon spheres (NSCS) with Co3O4 (NSCS-Co3O4). Hydrothermal reaction of saccharose with L-cysteine has been carried out followed by its carbonization. CSs, when used as support for conversion type materials provide efficient electron/ion transfer channels enhancing the overall electrochemical performance of the electrodes. Additionally, hetero atoms doped in carbon matrix alter the electronic properties, often increasing the reactivity of the carbon surface and reported to be effective for anchoring metal oxide nanoparticles. Consequently, the NSCS-Co3O4nanocomposites developed in this work exhibit enhanced and stable reversible specific capacity over the cycling. Stable cycling behavior is observed at 1 Ag-1 with 1285 mAhg-1 of specific capacity retained after 350 cycles alongwith more than 99% of coulombic efficiency. This material shows an excellent rate capability with specific capacity retained to 745 mAhg-1 even at a high current density of 5 Ag-1. Detailed DFT based calculations have revealed the role of doped support in controlling the volume expansion upon lithiatio
  • Sheena Agarwal, Shweta Mehta, Nivedita Kenge, Siva Prasad Mekala, Vipul Patil, T. Raja And Kavita Joshi*, Mixed metal oxide: A new class of catalyst for methanol activation, Applied Surface Science., , (2020).
    In this work, we propose a mixed metal oxide as a catalyst and demonstrate it's ability to not only activate the MeOH molecule upon adsorption but also dissociate O-H and one of it's C-H bonds. MeOH activation is compared on two prominent facets of \znalo~ viz. (220) and (311). While spontaneous O-H bond dissociation is observed on both facets, C-H bond dissociates only on the (311) surface. Multiple factors like atomic arrangement and steps on the surface, coordination of surface atoms, and their effective charges have a combined effect on MeOH activation. The (311) surface offers higher catalytic activity in comparison with (220) surface. Having a stepped surface, availability of multiple sites, and variation in the charge distribution are some of the reasons for better catalytic performance of (311) facet. Effect of orientation of MeOH with respect to the surface adds both, information and complexity to the problem. Observations pertinent to understanding this effect are also reported. A detailed analysis of atomic arrangement on the two surfaces provides a rationale as to why MeOH gets dissociated spontaneously on the mixed metal oxide. The promising results reported here opens up a new class of catalyst for research.
  • 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.
  • 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

  • Theory AND Computational Science

Contact Details

Kavita Joshi

Office: MSM, Near East Gate
Physical and Materials Chemistry Division
CSIR National Chemical Laboratory
Dr. Homi Bhabha Road
Pune 411008, India
Phone   +91 20 2590 2476
E-mail k.joshi@ncl.res.in