arXiv subjects

Kuntal Talit

Publications and source records attributed to Kuntal Talit.

4 recordsLinked to original sources

arXiv2026

TritonDFT: Automating DFT with a Multi-Agent Framework

Density Functional Theory (DFT) is a cornerstone of materials science, yet executing DFT in practice requires coordinating a complex, multi-step workflow. Existing tools and LLM-based solutions automate parts of the steps, but lack support for full workflow automation, diverse task adaptation, and accuracy-cost trade-off optimization in DFT configuration. To this end, we present TritonDFT, a multi-agent framework that enables efficient and accurate DFT execution through an expert-curated, extensible workflow design, Pareto-aware parameter inference, and multi-source knowledge augmentation. We further introduce DFTBench, a benchmark for evaluating the agent's multi-dimensional capabilities, spanning science expertise, trade0off optimization, HPC knowledge, and cost efficiency. TritonDFT provides an open user interface for real-world usage. Our website is at https://www.tritondft.com. Our source code and benchmark suite are available at https://github.com/Leo9660/TritonDFT.git.

cond-mat.mtrl-sci↗

arXiv2024

Resolving Discrepancies in Calculations of Mechanical Properties of CH\textsubscript{3}NH\textsubscript{3}PbI\textsubscript{3} Perovskites

The mechanical properties of hybrid perovskite materials are important for device flexibility, resistance to fracture, epitaxial growth, surface energetics of quantum dots, and induction or relief of stress in thin films due to thermal expansion and phase changes. These issues are particularly salient for solar cells in space applications. Nonetheless, few studies are available on the mechanical properties of the paradigmatic hybrid perovskite CH$_3$NH$_3$PbI$_3$ (MAPI). Experimental results are only available for the room-temperature tetragonal phase, and there are significant discrepancies among them. Results from density functional theory (DFT) are available for all three phases but have even larger discrepancies from each other and from experiments. To clarify the disorder in the literature, we have studied the elastic properties of all three phases in detail with DFT calculations. We have examined the effect of different aspects in calculation methodology such as use of energy or stress, the structure, exchange-correlation functionals, Van der Waals corrections, pseudopotentials, $k$-point sampling, and formulas for anisotropic elasticity and polycrystalline averages. Our results provide accurate reference values and an appropriate general methodology for elastic properties of metal halide perovskites.

cond-mat.mtrl-sci↗

arXiv2023

Quantifying Hidden Symmetry in the Tetragonal CH$_3$NH$_3$PbI$_3$ Perovskite

The assignment of an exact space group to the tetragonal CH$_3$NH$_3$PbI$_3$ perovskite structure is experimentally challenging and controversial in the literature. Average orientation of the methylammonium ion that gives symmetry to the experimental measurement is not captured in a static density functional theory calculation, although the quasi-I4cm and quasi-I4/mcm structures are commonly used in calculations. In this work we have developed a methodology to quantify the hidden symmetry of these structures using group theory, to enable use of symmetries in understanding spectroscopy and other properties. We study the approximate symmetry of vibrational modes, including analysis of degenerate representations, as well as the dielectric, elastic, electro-optic, Born effective charge, and Raman tensors and the dynamical matrix. Comparing to each subgroup of the full tetragonal D$_{4h}$, our results show that the quasi-I4cm is best described by the expected corresponding point group C$_{4v}$, whereas the quasi-I4/mcm (despite corresponding to point group D$_{4h}$) is best described by the lower symmetry C$_{2v}$. Our methodology can be useful generally for analysis of other soft hybrid materials or any approximately symmetric material.

cond-mat.mtrl-sci↗

arXiv2020

Stress effects on vibrational spectra of a cubic hybrid perovskite: A probe of local strain

Inhomogeneous strain may develop in hybrid organic metal-halide perovskite thin films due to thermal expansion mismatch with a fabrication substrate, polycrystallinity or even light soaking. Measuring these spatially varying strains is difficult but of prime importance for understanding the effects on carrier mobility, non-radiative recombination, degradation and other optoelectronic properties. Local strain can be mapped using the shifts in vibrational frequencies using Raman or infrared microscopy. We use density functional theory to investigate the effect of uniaxial strain on the vibrations of pseudo-cubic methylammonium lead iodide (CH$_3$NH$_3$PbI$_3$), and identify the vibrational modes most favorable for local strain mapping (86 cm$^{-1}$, 97 cm$^{-1}$, 1457 cm$^{-1}$, and 1537 cm$^{-1}$) and provide calibration curves. We explain the origin of the frequency changes with strain using dynamical matrix and mode eigenvector analysis and study strain-induced structural changes. We also calculate mode Grüneisen parameters, giving information about anharmonicity and anisotropic negative thermal expansion as recently reported for other phases. Our results provide a basis for strain mapping in hybrid perovskites to further the understanding and control of strain, and improve stability and photovoltaic performance.

cond-mat.mtrl-sci↗