Abstract: The central idea of Density Functional theory (DFT) is to describe many-particle systems, using single-particle density quantities as the basic variables. The concept of density spans over all the length and time scales. For microscopic quantum systems, it is the electron density which is used to describe the properties of atoms, molecules, clusters and solids. Although started with Thomas Fermi theory as early as 1927, DFT was formally born through the work of Hohenberg, Kohn and Sham in mid-sixties, and has now become a versatile tool for electronic structure theory, particularly for large systems.

Analogously, in the intermediate mesoscopic length scale, it is the particle number density which serves as the central variable, leading to effective Boltzmann like equations. This so called classical DFT has found wide applications in the area of soft matter physics. In the macroscopic length scale, besides the use of property densities as basic variables, leading to DFT in parameter space, interconnection with continuum theory, hydrodynamics etc are of special interest.

Description of the methodologies along these lines, with brief mention of illustrative examples of applications will be highlighted.

Thus, the talk will dwell on: (i) Concept of density across the length scales: Density functionals and the Machinery of DFT, (ii) Quantum (electronic) DFT: Hohenberg-Kohn-Sham formalism: Universal functionals: Exchange-correlation functionals: Approximations: LDA and beyond; Concept of iterative self consistent solution: Use of basis sets; Orbital based and orbital free DFT; Excited states and time-dependent situations. (iii) Classical (mesoscopic) DFT: Mermin theorem; Excess free energy functionals; Effective Boltzmann like distribution: Application to soft matter systems: DFT and phase transitions; Interconnection with PFM, MCT etc. (iv) Macroscopic DFT: Parameter space DFT; Interconnection with continuum mechanics and hydrodynamics. (v) Miscellaneous aspects of DFT: Concepts from DFT

References:

1. R.G. Parr and W. Yang (1989), Density Functional Theory of Atoms and Molecules, OUP.

2. S.K. Ghosh and B.M. Deb (1982), “Densities, Density Functionals and Electron fluids”, Phys. Rep. 92, 1-44.

3. N.H. March and B.M. Deb, (1987) The Single Particle Density in Physics and Chemistry, Academic Press.

Brief Bio-sketch:

Swapan K. Ghosh is currently Distinguished Professor at the UM-DAE-Centre for Excellence in Basic Sciences, University of Mumbai. Earlier, he worked at the Bhabha Atomic Research Centre for nearly forty years. He is specialized in Theoretical Chemistry research, at the interface of chemistry, physics and materials science, dealing with systems and phenomena at diverse length and time scales, covering both quantum and classical domain. His current research interests lie in multi-scale modeling of molecules and materials, stochastic and nano-thermodynamics, chemical concepts from DFT, soft condensed matter physics, etc. He received his Ph.D. from IIT, Bombay and was awarded D.Sc. (h.c.) by University of Kalyani. He is a Fellow of all the three National Science Academies of India and also of The World Academy of Science, Trieste, Italy (TWAS). He is also recipient of the TWAS Prize in Chemistry.

Abstract: There are many reasons for Density Functional Theory (DFT) to have established itself as the unchallenged workhorse for first-principles materials specific simulations --- its simple conceptual framework, practical elegance, and amenability to meaningful ramifications. DFT has proved itself to be extremely handy tool in understanding the physical and chemical properties of materials from bulk to nano, and also in designing novel materials with desired combination of properties [1]. In this Webinar, I shall try to provide an overview of the techniques being used to solve the Kohn-Sham equation for exploring various kinds of materials and their properties [2]. While plane-wave based methods are being widely used for tackling a large variety of problems, atom-centered (spatially localized) energy dependent basis functions such as Muffin-tin orbital methods [3,4] provide the possibility of transforming to a short-ranged tight-binding like basis via screening transformation [3,4]. This approach combines efficiency with accuracy and also helps extracting the chemical information in a transparent way. I shall also touch upon some recent developments on full potential implementation of this approach, that has been coupled with LDA+U, GW and the dynamical mean field theory (DMFT) [4,5]. The typical target audience for this Webinar would be Masters / PhD students, young researchers (including experimentalists who are desirous of using DFT codes) who want to have a working knowledge for using DFT based electronic structure methods, and also want to understand their capabilities and limitations.

References :

1. G.P. Das, “First-principles design of Materials”, in ‘Materials Research: Current Scenario and Future Projections’, Eds. R. Chidambaram and S. Banerjee (Allied Publishers, New Delhi, 2003) pp. 638-659.

2. R.M. Martin, “Electronic Structure : Basic Theory and Practical Methods”, Cambridge Univ Press (2004)

3. G.P. Das, ‘Introduction to Linear Band Structure Methods’, in Electronic Structure of Alloys, Surface and Clusters, A. Mookerjee and D.D. Sarma (Eds) Chapter-2 (Taylor & Francis, 2003).

4. H. Dreysse (Ed), ‘Electronic Structure and Physical Properties of Soids: The use of the LMTO Method’, in Lecture Notes in Physics,Vol 535, Springer, Berlin (2000); see articles in this Vol.

5. O.K. Andersen, ‘From Materials to Models: Deriving Insights from Bands’, in DMFT from Infinite Dimensions to Real Materials Modeling and Simulations, by E. Pavarini et al (Eds) Chapter-2 (2018).

6. Questaal: A package of electronic structure methods based on the LMTO technique, Dimitri Pashov, Swagata Acharya,…,Mark van Shilfgaarde, Comp. Phys. Commun. 249, 107065 (2020)

Brief Bio-sketch:

Prof. Gour Prasad Das is a condensed matter physicist and a materials scientist working as Visiting Professor in IIT Kharagpur. He specializes in first-principles simulation and design of materials from bulk to nano, with specific applications in materials science and nano-devices. He has used density functional based approach to calculate the electronic, magnetic, and thermodynamic properties of intermetallic alloys, epitaxial interfaces, multilayers, clusters, and low dimensional quantum structures. Prof. Das served as visiting scientist/faculty in a number of institutes viz. MPI Stuttgart, Virginia Commonwealth University, Richmond, IMR Sendai, UNSW Sydney. He has also spearheaded several research programmes nationally and internationally.

Abstract: In this Webinar, I plan to introduce the basics of Molecular Dynamics and will cover following topics. The emphasis the presentation will be informal but pedagogic. The emphasis will be on methodology.

1. Basics

2. Solving Newton’s eq. Verlet and velocity Verlet

3. Constant NVT ensemble

4. Maintaining Temperature (Nose without Derivation)

5. Simulated annealing with example of cluster (Open Boundary conditions)

6. Extracting Physics from trajectories.

7. Ab initio MD Marriage with DFT

8. Born-Oppenheimer versus Car-Parrinello Dynamics (Short presentation)

9. Introduction to non-adiabatic dynamics.

10. Some example – Time permitting

Brief Bio-sketch:

Prof. D G Kanhere is a condensed matter physicist. His main are of research are applications of ab initio molecular dynamics to physics of clusters, two dimensional materials magnetism. He has also contributed to Model Hamiltonian physics mainly Hubbard and t-j models using exact diagonalization technique. Presently he heads SCIENCE PARK, special initiative of SPPU for school children. He is a fellow of Indian academy of science and recipient of Meghnad Saha Award (UGC).

Abstract: Kohn-Sham density functional theory (DFT) calculations have been instrumental in providing many crucial insights into materials behavior and occupy a sizable fraction of world’s computational resources today. However, the stringent accuracy requirements in DFT needed to compute meaningful material properties, in conjunction with the asymptotic cubic-scaling computational complexity with number of electrons, demand huge computational resources for accurate DFT calculations. Thus, these calculations are routinely limited to material systems with at most few thousands of electrons, employing plane-wave discretization despite all its limitations which has remained the method of choice for many material science applications.

In this talk, I will present some recent advances made in the state-of-the-art for accurate DFT calculations -via- the development of DFT-FE, employing finite-element discretization (polynomial basis). This has enabled fast, scalable and accurate large-scale norm-conserving pseudopotential DFT calculations on material systems with tens of thousands of electrons while allowing for arbitrary boundary conditions and generality of material systems. This has been facilitated by (i) efficient and accurate spatially adaptive discretization strategies using higher-order finite-elements [1]; (ii) development of efficient and scalable numerical algorithms in conjunction with mixed-precision strategies for the solution of Kohn-Sham equations [1,2]; (iii) implementation innovations, both on many core and CPU-GPU hybrid architectures, that significantly reduce the data movement costs and increase arithmetic intensity [2]; and (iv) a configurational force approach to compute atomic forces and unit-cell stresses in a unified framework [3]. For material systems with 5000-20000 electrons, these methodological developments have resulted in DFT-FE providing a time-to solution on CPUs that is up to 10x faster than state-of-art plane wave codes for similar accuracy, while on GPUs speedups up to 60x are observed. The reported advance discussed in this talk has wide ranging implications in tackling critical scientific and technological problems by making use of the predictive capability of DFT calculations for large-scale material systems.

References:

1. https://doi.org/10.1016/j.cpc.2019.07.016

2. https://dl.acm.org/doi/abs/10.1145/3295500.3357157

3. https://doi.org/10.1103/PhysRevB.97.165132

Brief Bio-sketch:

Dr. Phani Motamarri received his PhD in the area of Computational Materials Physics from the Department of Mechanical Engineering at the University of Michigan, Ann Arbor, USA. His primary research interests include development and efficient implementation of mathematical techniques and real-space computational algorithms that can leverage the latest heterogeneous parallel computing architectures and future exa-scale machines for ab-initio modelling of materials. He is one of the key developers of DFT-FE --- an open-source code for massively parallel large-scale density functional theory calculations that was named as a finalist for 2019 ACM Gordon Bell Prize, the prestigious prize in scientific computing.

Abstract: First principles electronic structure calculations based on density functional theory (DFT) have emerged as a successful method in understanding and predicting properties of diverse class of materials. Often such calculations provide crucial insights into novel properties of materials either by themselves or in conjunction with experiments. In the present lectures, we shall consider a class of systems where methods based on density functional theory are not directly applicable and model Hamiltonian approaches are found to be more suitable. We shall discuss the genesis of such models and show that DFT based calculations play a crucial role to determine the realistic parameters of these models. We shall show how these DFT inspired model Hamiltonians help us to understand wide class of novel systems exhibiting spin gap, Rashba-effect, emergent spin-orbital liquid states etc.

Brief Bio-sketch:

Prof. Indra Dasgupta obtained his Bachelor’s and Master’s degree in Physics from Presidency College, Kolkata and IIT Kanpur respectively and PhD degree from Calcutta University based on a work done at S.N. Bose National Centre for Basic Sciences, Kolkata on the topic Electronic Structure and Transport in Quantum Disordered Solids. He subsequently worked at Max Planck Institute for Solid State Research in Stuttgart, IIT Bombay, IIT Kharagpur before joining Indian Association for the Cultivation of Science, Jadavpur Kolkata where he is presently a Senior Professor and Dean Academic (PhD). His research interests are electronic structure calculations of novel magnetic systems, strongly correlated systems, low-dimensional quantum spin systems, magnetic properties of materials at nano-scale and disordered systems.

Abstract:

Owing to its tremendous technological importance in renewable energy production and also for the fundamental physics of transport, there has been intensive study of thermoelectric properties of nanomaterials [1-3]. The thermoelectric properties of Graphene [4], h-BN and their heterostructures [5] were intensely studied recently. The temperature dependence of the electrical resistivity of Monolayer Graphene (MLG) was found to exhibit a different behaviour than found in the bulk material. Recent thermal conductivity measurements on monolayer- and bilayer-graphene (BLG) exhibit important connection to the lattice vibrational modes in these materials.

In this talk I shall first give a brief review of the importance of thermoelectricity as renewable energy source and illustrate the importance of thermoelectric transport parameters for thermoelectric devices. I shall then present first-principles Density Functional Theory (DFT) based electronic structure and Boltzmann transport theory (BTE) based methods, for both electron and phonon transport, to calculate the thermoelectric transport parameters for MLG and BLG and also for the heterostructures of Graphene and h-BN, without any adjustable parameters. I shall also discuss equilibrium molecular dynamics (MD) based method for studying thermal transport in heterostructures of Graphene and h-BN. In partcular, we shall discuss the length dependence of the lattice thermal conductivity in these materials and their possible application in thermoelectric devices. We show that the thermoelectric figure-of-merit (ZT) can be enhanced upon BN-doping and sample length reduction in graphene. Recently, we have studied thermoelectric properties of Transition-metal Dichalcogenides ZrX2 (X=S, Se, Te) monolayers, and found a large enchancement of ZT (~2) upon application of stress in these materials. These results [6-12] will be discussed in the light of available experimental measurements.

References:

1. A. Majumdar, Science 303 (2004) 777.

2. M. Zebarjadi et al, Energy Environ. Sci. 5 (2012) 5147.

3. D.G. Cahill et al, Appl. Phys. Rev. 1 (2014) 011305.

4. D. Efetov and P. Kim, Phys. Rev. Lett. 105 (2010) 256805.

5. C.C. Chen et al, Nano Research 8 (2015) 666.

6. R. D'Souza and S. Mukherjee, Physica E 69 (2015) 138.

7. R. D'Souza and S. Mukherjee, Physica E 81 (2016) 96.

8. R. D'Souza and S. Mukherjee, Phys. Rev. B 95 (2017) 085435.

9. R. D'Souza and S. Mukherjee, Phys. Rev. B 96 (2017) 205422.

10. R. D'Souza and S. Mukherjee, J. Appl. Phys. 124 (2018) 124301.

11. S. Ahmad, R. D’Souza and S. Mukherjee, Mater. Res. Expess 6 (2019) 036308.

12. R. D’Souza, S. Mukherjee and S. Ahmad, (to be published).

Brief Bio-sketch:

Dr. Sugata Mukherjee received his doctorate degree in Physics from Free University Berlin based on his theoretical work on surface science and physics of clusters. He has held research and visiting positions at Ecole Polytechnique Federale Lausanne (EPFL), Free University Berlin, Fritz-Haber Institute of the Max-Planck Society in Berlin and at Helsinki University of Technology in Espoo, before joining as faculty member at S.N. Bose National Centre for Basic Sciences in Kolkata. His research interests lie in the areas of – First principles Electronic Structure Calculation of electronic properties of Carbon and Boron Nitride based Nanomaterials, Ultrafast processes in Nanomaterials using time-dependent DFT methods and Physics and Chemistry of Nanoclusters. He is currently a guest editor of a special volume “Ordering, segregation & Order-Disorder transition in Alloys”, to be published by Inst of Phys (London) in Journal of Phys Cond Matter.

Abstract: Layered ternary transition metal (TM) tri-chalcogenides with the general formula MAX₃ (M=TM; A=Si, Ge or P; and X=chalcogen) have been known and characterized extensively for decades. Most of them are magnetic semiconductors, generating interest in their fundamental properties, They also have potential for various applications. With the current interest in 2D materials, exploration of these compounds has received a new lease of life. Some of these compounds have shown interesting magnetic transitions in two dimensions, and promising catalytic behavior in hydrogen evolution (HER) and oxygen evolution reactions (OER).

We have developed new insights into the electronic structure of some of the Mn and Fe based tri-chalcogenide compounds. In particular, we have been able to correctly describe the ground state of FePSe₃, which some earlier works failed to do. We have also explored a number of such compounds, both known and unknown, for their efficiency in HER.

The second part of my talk will be on cobalt-based clusters. Some Co-carbide nano-particles have shown unexpectedly large magnetic anisotropy energy (MAE), making them interesting candidates for permanent magnets without rare earth elements. However, a microscopic analysis of the factors determining MAE in these systems was lacking. We have tried to arrive at an easily computable predictor that determines MAE in Co₄A₂ clusters (A= group 14 or 15 elements), and possibly in other Co-based nano-materials.

References:

1. S. Chabungbam and P. Sen, PRB 96, 045404 (2017).

2. P. Sen and R. Chouhan (Elec. Str. https://doi.org/10.1088/2516-1075/ab942a).

3. A. Sen and P. Sen, PCCP 21, 22577 (2019).

4. P. Sen, K. Alam, T. Das, R. Banerjee and S. Chakraborty, J Phys. Chem. Lett. (DOI: 10.1021/acs.jpclett.0c00710).

Brief Bio-sketch:

Prof. Prasenjit Sen is a computational material scientist, currently professor at the Harish-Chandra Research Institute Allahabad, India. He is specialized in the study of surfaces and nano structures using first-principles electronic structure methods. He uses a combination of methods depending on the complexity of the problem at hand. These include density functional theory (DFT) as well as wavefunction-based methods viz. HF and QMC at one extreme and other quantum chemical methods in between. His current research interests include designing of permanent magnets without rare earth elements, development of efficient CO oxidation catalyst, and design of magnetic superatoms etc. Prof. Sen received his Ph.D. from IIT Kanpur in 1997. He was a regular Associate of the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy (2012-2017).

Abstract: Topological phases arise from the one-to-one mapping of the wavefunction in the Brillouin zone to topological spaces (Sⁿ) such as circles, torus, Mobius band, etc. Despite their material realizations, their material flexibility for applications has remained a grand challenge. In this talk, I will start with the introduction to the topological band theory. I will then discuss how to computationally engineer various topological insulators starting from basic ingredients such as spin-orbit coupling, quantum tunneling. In specific examples, I will show that a 3D topological insulator can be designed artificially via staking layers of simple 2D electron gases, or via interactions, and other means.

References:

1. New topological invariants in non-Hermitian systems, A. Ghatak, Tanmoy Das, Journal of Physics: Condensed Matter 31, 263001 (2019).

2. Colloquium: Topological band theory, A. Bansil, H. Lin, Tanmoy Das, Review of Modern Physics 88, 021004 (2016).

3. A pedagogic review on designing model topological insulators, Tanmoy Das, Journal of the Indian Institute of Science 96, 77-106 (2016).

Brief Bio-sketch:

Das is a condensed matter theoretical physicists working in the areas of strongly correlated materials, superconductivity, topological insulators, non-Hermitian quantum systems. He as written about 100 journal papers on these areas. Some of the key papers include Topological Band Theory published in Review Modern Physics in 2016. He has introduced new ideas such as spin-orbit density wave, valence-fluctuation driven attractive potential as a new mechanism of superconductivity, non-Hermitian superconductivity, momentum dependent density fluctuation theory. He has received many awards including Infosys Young Investigator Award in 2017.

Abstract: In this presentation I will briefly go through the computational module that we have developed to calculate the transport properties of semi-conducting materials using Rode 's algorithm. The present version of the module is interfaced with Vienna ab-initio simulation package (VASP) and uses a variety of electronic structure inputs derived from the Density functional theory (DFT). We have shown good agreement with the experimental results of a number of systems, such as CdS, ZnSe, AlGaAs2 and GaBP2. A comparison of the present method with the standard approach such as relaxation time approximation will be highlighted.

References:

1. Semi-classical electronic transport properties of ternary compound AlGaAs2: role of different scattering mechanisms Soubhik Chakrabarty, Anup Kumar Mandia, Bhaskaran Muralidharan, Seung Cheol Lee and Satadeep Bhattacharjee, Journal of Physics: Condensed Matter, 32, 135704, (2019)

2. Ab initio semi-classical electronic transport in ZnSe: the role of inelastic scattering mechanisms A.K. Mandia, R. Patnaik, B. Muralidharan, S.-C. Lee and S. Bhattacharjee, Journal of Physics: Condensed Matter, 31, 345901 (2019)

3. Gallium-Boron-Phosphide(GaBP2): a new III-V semiconductor for photo-voltaics, U. Kumar, S. Nayak, S.Chakrabarty, S. Bhattacharjee and S.C. Lee, Journal of Materials Science (2020)

Brief Bio-sketch:

Bhattacharjee works as head of the Research and Development unit of IKST Bangalore, which is a subsidiary of Korea Institute of Science and Technology (KIST), Seoul. He obtained PhD in physics from IGCAR Kalpakkam and University of Madras, and has expertise in the broad field of materials theory. He uses methods such as first-principles based calculations, spin dynamics, Monte Carlo simulations and to some degree analytical approach. His current research activity includes simulations of transport properties of III-V semiconductors, surface science, electronic, magnetic and thermoelectric properties of Heusler compounds, permanent magnets etc.

Abstract: Data driven machine learning methods in materials science are emerging as one of the promising tools for expanding the discovery domain of materials to unravel useful knowledge. In this talk, the power of these methods will be illustrated by covering three major aspects, namely, development of prediction models, establishment of hidden connections and scope of new algorithmic developments. For the first aspect, we have developed accurate prediction models for various computationally expensive physical properties such as band gap, band edges and lattice thermal conductivity. The prediction model for band gap and band edges are developed on 2D family of materials -MXene, which are very promising for a wide range of electronic to energy applications, which rely on accurate estimation of band gap and band edges. These models are developed with GW level accuracy, and hence can accelerate the screening of desired materials by estimating the band gaps and band edges in a matter of minutes. For the lattice thermal conductivity prediction model, an exhaustive database of bulk materials is prepared. By employing the high-throughput approach, several ultra-low and ultra-high lattice thermal conductivity compounds are predicted. The property map is generated from the high-throughput approach and four simple features directly related to the physics of lattice thermal conductivity are proposed. The performance of the model is far superior than the physics-based Slack model, highlighting the simplicity and power of the proposed machine learning models. For the second aspect, we have connected the otherwise independent electronic and thermal transport properties. The role of bonding attributes in establishing this relationship is unraveled by machine learning. An accurate machine learning model for thermal transport properties is proposed, where electronic transport and bonding characteristics are employed as descriptors. In the third aspect, we have proposed a new algorithm to develop highly transferable prediction models. The approach is named as guided patchwork kriging, which is applied for prediction of lattice thermal conductivity.

References:

1. Chemistry of Materials 30, 4031, 2019

2. Journal of Physical Chemistry Letters 10, 780, 2019

3. Chemistry of Materials, 31, 5145, 2019

4. Journal of Materials Chemistry A 8, 8716, 2020

5. Journal of Physics: Materials 3, 024006, 2020

Brief Bio-sketch:

Prof. Abhishek K. Singh is currently an Associate Professor in Materials Research Centre at IISc, Bangalore. He did his PhD from Institute of Materials Research, Tohoku University, Japan. He was a JSPS Postdoctoral fellow. He has also worked as postdoctoral research associate at University of California Santa Barbara, and Rice University, Houston, USA. His group is leading an effort in designing materials for target applications using data-driven methods. His group has established India’s first computational materials database aNANt. He is currently leading the materials informatics initiative of IISc (MI3). Prof. Singh has published ~140 papers. His work has received ~ 5132 citations and his current h-index is 39. He is a recipient of martials research society of India medal in 2014, distinguished lectureship award of chemical society of Japan in 2020.

Abstract: In this talk, I will discuss methods development for two different (unrelated) applications: (a) High-throughput materials discovery/ machine learning thereof and (b) thermal transport in semiconductors. In the first part, I will discuss about spacegroup-symmetry-based structural prototype generation for high-throughput materials discovery. In the second part, I will discuss some of the aspects of thermal conductivity prediction for semiconductor crystalline materials from DFT calculations.

Brief Bio-sketch:

Dr. Ankit Jain obtained his Bachelor degree in Mechanical Engineering from Indian Institute of Technology, Kanpur, India in 2011. After finishing his bachelors, he joined Ph.D. program in the mechanical engineering department at Carnegie Mellon University under the supervision of Prof. Alan McGaughey. After finishing his PhD in 2015, Dr. Jain worked with Prof. Edward Sargent from University of Toronto and Prof Jens Norskov from Stanford University as a postdoctoral fellow. In April 2019, Dr. Jain joined the mechanical engineering department at IIT Bombay where he is leading Materials Simulation Research Group on methods development for thermal transport, high-throughput materials discovery, and catalytic applications.

Abstract: In this webinar talk, I would like to present a three-fold research activity interconnected with a common string “Energy”. At the beginning, a general overview on how materials modelling based on Density Functional Theory (DFT) formalism has taken the driving seat to envisage vivid energy materials in the scientific community will be demonstrated. The first part would be dedicated to the fundamental mechanism for the solar irradiated water splitting in photocatalytic materials with the future prospect of Non-linear Poisson Boltzmann Solver development for the heterogenous catalytic mechanism. The relevant exploration of novel 2D materials [1 - 5] and their applications in such catalytic mechanism, that consists of Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER), from a DFT based theoretical perspective. In the next part of my talk, the working principles behind the next generation Hybrid Perovskites Solar Cells [6 - 8] would be presented in connection to the High-throughput Screening based Rational Design of highly efficient and stable Photovoltaic materials. Our recent finding on Rashba-Dresselhaus effect in mixed phase hybrid perovskite solar cell with 22.1% efficiency would also be highlighted in this respect. The final part of the talk would be devoted to the fundamental understanding of our recently developed interface between Hybrid Eigen-vector Following (EF) formalism and DFT to predict the Transition Pathway without the prior knowledge of adjacent minima. I would conclude my talk with the implication of our developed interface to envisage ion migration corresponding to the structural phase transformation in polyanionic cathode materials [9, 10] and the next generation Solar Thermal Fuels.

References:

1. R. Majee,.., Sudip Chakraborty, et al. Angewandte Chemie, 59, 2881 (2020).

2. P. Sen,.., Sudip Chakraborty, J. Phys. Chem. Letters, 11, 3192 (2020).

3. J. Yang, .., Sudip Chakraborty* et al. ACS Nano, 13, 9958 (2019).

4. D. Saraf, Sudip Chakraborty* et al.Nano Energy, 49, 283 (2018).

5. A. Guha,.., Sudip Chakraborty* et al. ACS Catalysis, 8, 6636 (2018).

6. Sudip Chakraborty* et al. ACS Energy Letters - Perspective, 2, 837 (2017).

7. H. Arfin,..,Sudip Chakraborty* et al. Angewandte Chemie, 59, 1(2020).

8. S. Krishnamurthy,.., Sudip Chakraborty*, Advanced Optical Materials, 17, 1800751 (2018).

9. W. Teeraphat, Sudip Chakraborty* Journal of Materials Chemistry A, 17446 (2019).

10. W. Teeraphat, J. Thienspert, Sudip Chakraborty* et al. Nano Energy, 55, 123 (2018).

Brief Bio-sketch:

I am currently leading MATES (Materials Theory for Energy Scavenging) Group, embedded in Discipline of Physics, IIT Indore as Assistant Professor of Physics. My current group consists of 6 Ph.D and 4 Project students. After my PhD in modelling quantum dots for efficient solar cell, I moved to Max Planck Institute, Düsseldorf in early 2011 as Max Planck Postdoctoral Fellow. I was involved in developing Poisson-Boltzmann solver for DFT code dealing with solid-liquid interface and new technique of transition pathway prediction. In early 2013, I joined Uppsala University and worked there till February, 2019 as a Senior Researcher, while 4 Ph.D students got their degree under my supervision, before I joined IIT Indore. I primarily work on Materials Modelling for Hybrid Perovskite Solar Cells, Catalysis and Battery. I have served as potential reviewer for European Research Council (ERC) Advanced Grant and National Science Funding (NSF), while I was the co-chair of three consecutive European Materials Society (EMRS) Fall Meeting between 2014 and 2016. I have been invited to be the Guest Editor for two International journals: Frontiers in Chemistry and Catalysts. Presently, I have 94 International publications, having total 512 Impact Factors, with 1880 Citations, 25 h-index.

Abstract: Two-dimensional transition metal dichalcogenides (TMDs) dominate global research because of its layer-dependent properties, strong photoluminescense (PL), and high photoresponsivity for optoelectronic devices. In such devices the TMDs materials and the type of substrate is the major concern to get maximum efficiency and stability of the devices. Among all TMDs, MoS₂ is prospective 2D material for solar cells because of its direct band gap in monolayer around 1.8eV (690 nm), low dark current, and ideal candidate for tandem cells, which achieve highest power conversion efficiencies. The properties can be tuned by engineered the inter-facial region of the vdW hetrostructures.

The origins of photon absorption capability of vdW heterostructures are not completely understood. The correlation of quantum confinement, non-linearity in exchange-correlation functional and hybridization dependent interstitial potential with absorbance and efficiency is still an unanswered question. The similar value of non-linearity in the exchange and correlation potential is observed for all the 2D hetrostructures. Whereas different value of interstitial barrier potential is observed, means it govern the interlayer interaction. In this work, using first-principles approach, we provide a comprehensive study to show the effect of vdW interaction on optical and electrical characteristics of device and its origin.

The work is done through collaboration with Himanshu Saini, M. V. Jyothirmai, Umesh V. Waghmare.

References

1. Physical Chemistry Chemical Physics, 2020, 22, 2775-2782.

2. Scientific Reports, 2017, 7, 4505.

3. Mater. Horiz., 2017, 4, 274-280

Brief Bio-sketch:

Prof. Ranjit Thapa is currently Professor and Chair of Department of Physics, SRM University-AP. Prof. Ranjit’s research works are primarily focused on First-principles theory-based investigation of low dimensional and Pt-alloy based materials as a catalyst for Oxygen reduction reaction (ORR), OER, HER, CO oxidation, and CO2 reduction, Nitrogen reduction and absorber materials for solar cells. The main contributions are: “Bond Exchange Spillover Mechanism”, “Homonuclear B-B and B-B-B bond as catalytic center”, “inverse catalyst” and “electronic and structural descriptor”. He received the Young Associate Award in year 2016 by Indian Academy of Science, Bangalore for his outstanding research in the area of Computational Materials Science and was also chosen for BRNS’ Young Scientist’s Research Award (YSRA) in year 2018. Prof. Thapa has published ~84 research articles. His work has received ~ 2050 citations and his current h-index is 23.

Abstract: In thermoelectrics, severe plastic deformation giving rise to grains is employed by various sintering techniques which are essentially methods to consolidate powdered metal alloys. It has been found that thermoelectric figure of merit ZT is enhanced in nanostructured grains with small misorientations. It has also been observed that nanocomposites such as optimally doped Bi2Te3 and its solid solution with Sb2Te3 and Bi2Se3 and silica powder can enhance ZT. These grains and nanoinclusions are of nanometer to micrometer sizes for which first principle calculations and molecular dynamics based calculations become computationally too expensive. Therefore, not only there is a need to understand thermal transport across interfaces, grain boundaries and naoninclusions using known methods, but a mutiscale modeling of Boltzmann Transport Equation (BTE) will also help understand thermal and electrical transport across all these defects and composites involving several scales. Moreover, the evolution of grain boundaries during the whole thermomechanical process makes the thermal transport a complex phenomenon which can also help optimize ZT. The talk will involve some early attempts for developing a multiscale framework in which the phonon information coming from molecular dynamics/DFT simulations will be coupled with finite element methods for solving BTE which has advantages such as constructing a well defined boundary solution to be used to study thermal transport across the grain boundaries or phase and interface boundaries for nanoinclusions.

Brief Bio-sketch:

Dr. Amit Singh is teaching at Dept of Mechanical Engineering, IIT Bombay from November 2018. He received his Masters in 2011 and a PhD in 2015 from the Dept of Aerospace Engineering and Mechanics, University of Minnesota, under the guidance of Prof Ellad Tadmor, where he studied multiscale problems in heat conduction. Later he joined Mechanical Engineering, Northwestern University, as a postdoctoral fellow in 2016 where he worked with Prof Sinan Keten, Prof W. K. Liu and others on soft matter and graphene. Then he joined Prof Romesh Batra’s group at Dept of Biomedical Engineering and Mechanics, Virginia Tech as adjunct faculty. Dr Amit Singh is mostly interested in understanding continuum properties of matter from atomistic point of view. Once the basis of these continuum properties are revealed from the models at atomic, molecular and coarse-grained levels, his interest revolves around finding interesting mechanical, thermal, electrical and magnetic properties which can help design new materials and composites. He has been among the early developers of the Knowledgebase of Interatomic Models (https://openkim.org/). Presently he is interested in multiscale and statistical modeling of thermal transport, statistical and continuum modeling for mechanics of muscle contraction and tumor growth, fracture and grain boundaries in graphene, finite element modeling of fatigue in Titanium alloys, mechanical, thermal and electrical properties of polymers through multiscale methods and homogenization and finding analogies between solid mechanics and gravitational field equations. More about his work can be found here: https://amitsinghsiteblog.wordpress.com/

Abstract: Thermoelectrics are viable alternative towards achieving a green energy economy. First principles density functional theory calculations may aid to the issue of cost effective deployment of efficient thermoelectric materials by enabling a rapid screening prior to their synthesis in the laboratory. On the other hand such calculations may reveal the pathways to predict the complex interplay of underlying electronic and vibrational transport phenomena. Thermoelectric solids are generally referred to have a cage like structure of "host" enclosing "guest" atoms, whereby the electronic and vibrational transport can be decoupled by means of "host" and "guest" respectively. Using the simple binary [1,2] and complex ternary clathrates [3,4] as examples, we unravel the role of rattling of guest, mutual coupling of guest and host, and implications of defects on the charge and heat transport phenomena of this material class. Our study reveals the interplay of materials phenomena that goes beyond the usual concepts in this field. The vibrational transport phenomena is analyzed using indigenously developed python program package, which has been successfully employed to calculate the effect of doping on the thermal conductivity of the Heusler material class [5].

References:

1. Amrita Bhattacharya*, Christian Carbogno, Bodo Bohme, Michael Baitinger, Yuri Grin, and Matthias Scheffler. “Formation of vacancies in Si/Ge Clathrates: The importance of broken symmetries”, Phys. Rev. Lett. 118, 236401 (2017).

2. Amrita Bhattacharya*, The origin of glass-like phonon dynamics in binary Si and Ge clathrates-I , Journal of Materials Chemistry C, 7, 13986 (2019).

3. Amrita Bhattacharya* and Saswata Bhattacharya. Unraveling the role of vacancies in the potentially promising thermoelectric clathrates Ba8ZnxGe46-x-y□y clathrates. Phys. Rev. B, 94, 094305 (2016).

4. Amrita Bhattacharya*, Deviation from guest dominated glass like lattice dynamics in prototypical ternary Ba8NixGe46−x−y▢y clathrates, y clathrates, J. Phys. Cond. Matter, 32, 175502 (2020).

5. Nagendra S. Chauhan, Bhasker Gahtori, Bathula Sivaiah, Subhendra D. Mahanti, Ajay Dhar, and Amrita Bhattacharya*, "Modulating the lattice dynamics of n-type Heusler compounds via tuning Ni concentration" Appl. Phys. Lett., 113, 013902 (2018).

Brief Bio-sketch:

Amrita has done her PhD in computational materials science from Indian Association of the Cultivation of Science, Kolkata, India. She has carried out her post doctoral research as a Max Planck scientist in Fritz Haber Institute of the Max Planck Society, Berlin, Germany for a period of about four years. Following which, she has worked as a DST Inspire faculty in CSIR National Physical Laboratory, India. She is currently working as an Asst. Prof. in the MEMS Dept. of IIT Bombay, where she joined in late 2017. The main research thrust of her group is to analyze the charge and heat transport phenomena in solid using different ab initio techniques. She also uses different statistical machine learning models to predict properties of materials for their quintessential application.

Brief Bio-sketch:

Dr. Saswata Bhattacharya did his PhD from IACS Kolkata. Following this he was a Max Plack post doctoral fellow in the Fritz Haber Institute of the Max Planck Society for three years. He joined IIT Delhi as assistant professor on 2015, where he is leading the DISCERE group that works in inter-disciplinary areas of condensed matter physics with broad research interest in first principles based simulation of designing new materials and understanding their properties using state-of-the-art density functional theory. His has published more than 50 reasearch articles in international peer review journals, which has taken his h index to 19 with 1135 citations.

Abstract: Taking as axiomatic the existence of differentiable field quantities like density, displacement, strain and stress, and assigning locally averaged properties to material points, continuum mechanics has been spectacularly successful in solving boundary value problems in a given domain under suitable assumptions on constitutive behaviour. Nevertheless, matter and material response are not infinitely divisible, and continuum modeling may lose relevance when the domain size in not large compared to the characteristic length scale. In particular, when at least one spatial dimension is smaller than about 100 nm, certain aspects, typically negligible at the macroscale, start to gain prominence. One of these is surface effects caused by higher energetic atoms on the free surface. This talk will discuss surface energy, surface elasticity and friction between sliding surfaces at the nanoscale. Some recent results will be presented.

Brief Bio-sketch:

Baidurya Bhattacharya (BTech IIT Kharagpur 1991 and PhD Johns Hopkins 1997) is Professor of Civil Engineering at IIT Kharagpur. His area of work is probabilistic mechanics and computational materials science. After completing his doctoral studies, Bhattacharya continued as a Post-Doc at Johns Hopkins, worked as an R&D engineer at the American Bureau of Shipping, Houston TX, and taught at the University of Delaware and Stanford University before returning to his alma mater in 2006. He held the position of Chairman Civil Construction and Maintenance and currently serves as the Dean of International Relations at IIT Kharagpur. He was elected Fellow of the Indian National Academy of Engineering in 2016 and a Fellow of the American Society of Civil Engineers in 2018.