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My Research Highlights
Studying the role of defects on the thermal transport in 3D and 2D materials 

 

I am working on the theoretical investigation of the thermal transport in 3D and 2D materials with defects. My work is in close collaboration with different international experimental groups, where I have contributed to the study of thermal transport in experimentally found novel 2D materials. I have carried out an elaborative study of the role of different antisite defects in half Heusler ZrNiSn based thermoelectric material. I have also unveiled the exceptional effect of Boron doping on the thermal conductivity of cubic SiC. Interesting results were obtained in all these studies which have have shaped into publications in reputed peer-reviewed journals such as: Phys. Rev. Lett., 119, 075902 (2017); J. Mat. Chem. A, 4, 15940 (2016); Appl. Phys. Lett., 109, 131907 (2016).

Phonon-defect scattering rates in half-Heusler NiSnZr showning the dominant effect of Ni/vacancy antisite defects over Sn/Zr.
Calculated thermal conductivity of cubic SiC with defects from first principles.Figure shows good agreement with experiments (symbols).
Profile of phonon scattering rates around a dual-defect (Sn/Zr antisites in NiSnZr) calculated with almaBTE.
Representation of bond length variation (propertional to bond width) with inclusion of Boron defect in cubic SiC showing DX centre. 
Development of almaBTE code
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I am also involved in extensive development of almaBTE, a code developed in-house for calculating thermal transport in structured materials. My main contribution is in the development of defect scattering routines in almaBTE to calculate the phonon-defect scattering using Green’s function approach. The code has been tested for numerous materials and the results show good agreements with the corresponding experimental outcomes. The code has been released recently (www.almabte.eu) [Computer Physics Communications, (almaBTE code) 220C, 351, 2017)].

Figure showing the important components of force constants matrix up to second neighbors interactions. Only those components can be modelled. 
Development of Simplified Models for Simulation of thermal properties.

 

My PhD comprised of developing simplified models to simulate thermal properties (thermal expansion and conductivity) for thermoelectric materials. I have developed a model [J. Phys. Condensed Matter, 25, 365403 (2013)] for the lattice dynamics of SixG1-x alloys. The model is short ranged and includes interactions up to second neighbors only. The model reliably reproduces thermal expansion and shows transferability to SixGe1-x random alloys. This work shows that the long ranged thermal properties could be modelled correctly even with the short ranged potentials.

Tight-Binding modelling
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I also developed an orthogonal tight-binding model [Phys. Rev. B 93, 155203 (2016)] for Si, with a focus of calculating thermal properties. This tight-binding model is based on the systematic down-folding procedure to obtain the orbital interaction parameters from DFT. The model is short-ranged and simple with less parameters, and is tested for the reproducibility of thermal conductivity and other thermal properties of Si in comparison to DFT and experiments. A good transferability to the other geometries (simple cubic, beta-tin, Si clathrates) is also shown by DFT obtained model parameters.

Energy-volume curves for different structures of Si calculated with our Tight binding model (dashed lines) and compared with DFT (solid lines).
Transferability test showing good agreement of phonon dispersion for complex clathrate structure of Si between our model (magenta) and DFT (black). 
Obtained Research Funds 
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  • Research grant under ISRO RESPOND project scheme (Oct, 2019 - Sept, 2021)

  • DST-INSPIRE research grant (July, 2018 - June, 2023)

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Ongoing Research Projects 
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Some of my current research projects include:

  • Machine Learning for the prediction of new layered materials. 

  • Understanding transport properties of new 2D materials. 

  • Further development of almaBTE to integrate defect scattering routines with different thermal conductivity solvers implemented in the software. 

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Computational tools

Currently used softwares and programing languages in the group:

  • DFT, MD and phonon packages: QE, LAMMPS, Phonopy, ShengBTE, almaBTE,

  • Atomic visualization packages: Atomic Simulation Environment (ASE), VESTA, VMD, Jmol, Ovito. 

  • Programming Languages: Python scripting, C, C++, bash scripting.

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