Group News
14 Oct 2021

Our recent work on benchmarking the interlayer spacing, intercalation voltage, thermodynamic stability, and electronic properties of redox-active layered transition metal oxides was published today in Physical Chemistry Chemical Physics. We benchmarked a total of eight exchange-correlation functionals, namely the strongly constrained and appropriately normed (SCAN), Perdew-Burke-Ernzerhof (PBE), the corresponding Hubbard U corrected functionals, and with or without van der Waals corrections. Our work will benefit in selecting the right theoretical framework for accurately modelling intercalation-based cathodes for Li-ion batteries and beyond. The paper was written by Ms. Olivia Long (Stanford University), Dr. Sai Gautam Gopalakrishnan, and Prof. Emily A. Carter (University of California Los Angeles and Princeton University).

31 Aug 2021

August 2021 had four new entrants to the SAI MATerials group, including Anooj Sathyan (top left in picture), Swathilakshmi (top right), Ankur Srivastava (bottom left), and Vijay Choyal (bottom right). Anooj will be pursuing his Bachelors thesis research (on machine learning related topics), while Swathi will be an intern learning the ropes of density functional theory calculations. Ankur is a Ph.D. student, co-advised with Prof. Aloke Paul (Materials Engineering, Indian Institute of Science) and will focus on diffusion studies. Vijay Choyal is the first postdoctoral researcher of the group, who will also be an Institute of Eminence fellow. The group wishes a productive stay for all four new members.

16 Aug 2021

Recent work on the building a robust and physically-intuitive machine learning model on predicting oxygen vacancy formation energies in ternary oxide perovskites was published today in Journal of American Chemical Society. The model uses metrics such as solid-state reduction potentials, crystal bond dissociation energies, energy above the convex hull, and the band gap at Gamma point, thus allowing for equivalent models to be built with either experimental or theoretical data or both. The paper was written by Dr. Robert Wexler (Princeton University), Dr. Sai Gautam Gopalakrishnan, Dr. Ellen Stechel (Arizona State University) and Prof. Emily A. Carter (University of California Los Angeles).

8 Aug 2021

Dr. Sai Gautam Gopalakrishnan will deliver a (virtual) talk, as part of the Aug-Dec 2021 seminar series organized by the Department of Chemical Engineering, Indian Institute of Science. The talk will be on “combining density functional theory and thermodynamic frameworks for materials design in energy applications” and the abstract is provided below. The talk will be on 12th Aug, 2021 (Thursday), 4-5pm Indian Standard Time. Please use this link to join in.

Abstract

Updating our energy infrastructure, in terms of moving away from fossil-fuel-based sources to renewable and sustainable sources, is a critical need to ensure that the dramatic effects of climate change are mitigated. However, the performance of devices that are employed in energy generation, storage, or harvesting applications are typically limited by the materials that are used. Hence, it is important to design novel materials that can improve the efficiencies of such energy-based applications. Computational materials science, based on density functional theory calculations and supplemented by thermodynamic and kinetic principles and machine learning, can accelerate the process of materials design, especially in energy applications.

In the first part of my talk, I will present some of our recent work on unearthing promising electrode materials in Ca-ion battery systems. While the state-of-the-art energy storage systems are Li-ion batteries, they are approaching the practical limits of their achievable energy densities apart from other safety, cost, and supply-chain constraints. In this respect, Ca-based intercalation systems can offer a viable alternative, since electrochemical devices based on Ca can achieve energy densities equivalent to (or better than) Li-ion systems, and can alleviate the cost and safety constraints. However, the lack of Ca-ion intercalation electrodes (i.e., cathodes) has so far hindered the practical development of Ca-ion batteries. In this work, we search through Ca-containing ternary oxides and other chalcogenides, which can function as Ca-ion cathodes. Specifically, we use constraints on charge-neutrality, redox-activity, and thermodynamic stability to identify an initial list of candidates, following which we perform nudged elastic band calculations to estimate migration barriers for Ca-diffusion in the candidate structures. Importantly, we identify two promising materials, namely CaV2O4 and CaNb2O4, that exhibit reasonable migration barriers, intercalation voltage, and thermodynamic stability upon Ca (de)intercalation, Finally, we also update a set of design rules that can be used to identify more intercalation systems for Ca-ion batteries.

In the second part of the talk, we will explore the chemical space of Ca-Ce-M-O (M=3d transition metal) oxide perovskites, which have the potential to exhibit higher entropies of reduction, and hence higher productivity with respect to H2 or CO generation in solar thermochemical (STC) water/CO2 splitting applications. STC processes have the potential to be an efficient way to generate renewable fuels or fuel precursors using concentrated sunlight. Specifically, an STC process can use redox-active, off-stoichiometric transition-metal oxide substrates to split water and CO2, generating syngas, H2 and CO. Specifically, we explore systems with Ca and/or Ce occupying the A site and M occupying the B site within an ABO3 framework, using DFT-based calculations. While we consider only Ca and/or Ce on the A-site because of their similar size and the potential redox-activity of Ce, we evaluate all 3d transition metals except Zn on the B-site (Zn+3 is uncommon in solids). We evaluate the oxygen vacancy formation energy (~enthalpy of reduction in an STC process), electronic properties, and thermodynamic stability of ternary Ca-M-O, Ce-M-O, and quaternary Ca-Ce-M-O perovskites, identify promising candidates, and extract metrics that govern the enthalpy and entropy of reduction that are key to improving STC efficiencies.

17 Jul 2021

Wang and Juefan’s paper on computationally screening for Ca posititve electrodes was published today in Chemistry of Materials. Searching through the chemical spaces of oxides and chalcogenides, the study used a set of robust filtering criteria, including redox-activity, thermodynamic stabiity, and charge-neutrality to arrive at a set of 10 candidate compounds, which were further evaluated using density functional theory-based calculations. Importantly, the study found two previously unreported candidates, namely, CaV2O4 and CaNb2O4, both of which exhibit fair Ca mobility. Finally, the paper unearthed a set of updated design principles for constructing facile ionic conductors. The work was led by Prof. Piero Canepa (National University of Singapore), in collaboration with Dr. Sai Gautam Gopalakrishnan.

1 Jul 2021

The SAI MATerials group welcomes Tanmay Mohan Bhagwat, who will be a research intern. Tanmay graduated with a Bachelors in Mechanical Engineering from the Birla Institute of Technology and Science, Pilani (Hyderabad campus) in 2021. He will be working on computationally modelling photo(electro)catalysts.

21 Apr 2021

Dr. Sai Gautam Gopalakrishnan will deliver a (virtual) talk, as part of the “EN05.05 – Solar Thermochemical Water Splitting II” symposium at the “Materials Research Society (MRS) Spring Meeting,” 2021. He will speak about his post-doctoral work of identifying simultaneously redox-active oxide perovskites for solar thermochemical water splitting applications. The talk will be between 8.10-8.25 AM Indian Standard Time on April 21 (Wednesday). To join the talk, use your MRS credentials to login at the meeting link. The talk will also be available on-demand for a few weeks after the meeting is over. The slides presented will also be uploaded on the group website soon.

2 Apr 2021

The SAI MATerials group welcomes Abhirup Bhadra, who will is a visiting doctoral student from the School of Chemical Engineering in University of New South Wales. Abhirup’s research involves both experimental and computational aspects of all-solid-state batteries and he is pursuing his Ph.D. under the guidance of Dr. Dipan Kundu. Prior to the start of his Ph.D., Abhirup graduated with a Masters in Chemistry from Indian Institute of Technology Kharagpur. The group wishes Abhirup a pleasant stay and a sound execution of the computational aspects of his research while he is around.

1 Apr 2021

Recent work on the discovery of a new chalcogenide semiconductor, Cu2CdGeS3Se, which shows promising thermodynamic stability, optimal band gap, and robust resistance to formation of deep-trap-inducing defects, was published today in Journal of Materials Chemistry A. The paper was written by Dr. Robert Wexler (Princeton University), Dr. Sai Gautam Gopalakrishnan and Prof. Emily A. Carter (University of California Los Angeles).

17 Mar 2021

Dr. Sai Gautam Gopalakrishnan will deliver a (virtual) talk, as part of the “Energy Research – Solar Energy” symposium at the “American Physical Society (APS) March Meeting,” 2021. He will speak about his post-doctoral work of finding oxide perovskites with simultaneous cation redox activity for solar thermochemical water splitting applications. The talk will be between 2.30-2.42 AM Indian Standard Time on March 17 (Wednesday) or, equivalently 4-4.12 PM Central Daylight Time on March 16 (Tuesday). To join the talk, use your APS credentials to login at the meeting link.


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