Publications

Predicting Crystal Volumes

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Iek-Heng Chu’s paper on “Predicting the Volumes of Crystals” has been published in Computational Materials Science. In this collaborative work with the Hacking Materials group, we developed two schemes for predicting crystal volumes. Accurate crystal volume estimates are immensely useful for further experimental analysis, or to generate initial guesses for electronic structure optimizations. The volume prediction algorithms are implemented in the open-source pymatgen software.

Publications

First-order Interfacial Transformations in GB

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Hui Zheng is a co-author on a recently published article in Physical Review Letters on “First-Order Interfacial Transformations with a Critical Point: Breaking the Symmetry at a Symmetric Tilt Grain Boundary”. A collaboration with the Luo group, this work examines symmetry breaking in the ∑5 (210) GB using a modified genetic algorithm with Monte Carlo and molecular dynamics simulations. Read more about this work here.

Announcements

Sr2LiAlO4 – A novel earth-abundant phosphor with excellent color quality

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Our paper on “Mining Unexplored Chemistries for Phosphors for High-Color-Quality White-Light-Emitting Diodes” has been published in Joule. Using supercomputers and data mining, we identified Sr2LiAlO4, the first known Sr-Li-Al-O quaternary crystal, as a highly promising phosphor material in low-cost, high-color-quality white LEDs. Eu2+ and Ce3+-activated Sr2LiAlO4 phosphors exhibit broad green-yellow and blue emissions, respectively, with excellent thermal quenching resistance of > 88% intensity at 150oC. A prototype phosphor-converted white LED utilizing Sr2LiAlO4-based phosphors yields an excellent color rendering index exceeding 90. This work is a collaboration between the Materials Virtual Lab (UCSD), McKittrick group (UCSD) and Im group (Chonnam University). The lead authors are Zhenbin Wang, Jungmin Ha and Yoon Hwa Kim. More information about this work can be found in the Jacobs School of Engineering News as well as Science Daily, Phys.org, etc.

Publications

Zr strengthening of MoSi2

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Hui Zheng’s first paper on “Role of Zr in strengthening MoSi2 from density functional theory calculations” has just been published in Acta Materialia. MoSi2 is an important intermetallic with excellent oxidation resistance at high temperatures. However, “pesting” by oxygen limits its application at intermediate temperatures. Using DFT calculations, we show that Zr nanoparticles act as a getter for oxygen, and in the process, significantly strengthens MoSi2 interfaces and grain boundaries. We also use the Materials Project to efficiently screen for other potential getter elements using simple thermodynamic descriptors, a general approach that can be extended to other alloy systems of interest.

Publications

Probing Interfacial Reactions in All-solid-state Na-ion Batteries

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Hanmei’s first paper on “Probing Solid-Solid Interfacial Reactions in All-Solid-State Sodium-ion Batteries with First Principles Calculations” has just been published in Chemistry of Materials. In this comprehensive work, we show how explicit AIMD models can lead to different predictions of interfacial reaction products from simple thermodynamic approximations. Specifically, SO4 formation is predicted to be favored over PO4 formation at the interface between NaCoO2 and Na3PS4. We also identified several promising new candidates for buffer materials that potentially show lower reactivity with common electrodes and solid electrolytes.

Publications

Halide migration in Hybrid Organic-Inorganic Perovskites

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Zhuoying Zhu is a proud co-author on a recent publication titled “Direct Observation of Halide Migration and its Effect on the Photoluminescence of Methylammonium Lead Bromide Perovskite Single Crystals” published in Advanced Materials. In this collaborative effort with the Fenning group@UCSD, halide ion migration and its corresponding effect on photoluminescence are observed in relation to changes in the applied electric field in  single crystals of methylammonium lead bromide (CH3NH3PbBr3). Higher local Br concentrations is shown to be correlated with superior optoelectronic performance. Nudged elastic band calculations (Zhuoying’s contribution) show that lower barriers for vacancy migration in directions that contains a component along the C-N alignment axis, in good agreement with the experimental observations.

Publications

Accurate Machine-learned Potential for Molybdenum

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Chi’s paper on “Accurate force field for molybdenum by machine learning large materials data” has just been published in Physical Review Materials. This work addresses a crucial gap in the available force field for Mo. We will show that by fitting to the energies, forces, and stress tensors of a large DFT dataset on a diverse set of Mo structures, a Mo Spectral Neighbor Analysis Potential (SNAP) model can be developed that achieves close to DFT accuracy in the prediction of a broad range of properties, including elastic constants, melting point, phonon spectra, surface energies, grain boundary energies, etc. Examples and parameters of the new potential can be obtained at our Github page.

Publications

VOPO4 polymorphs as Li/Na-ion battery cathodes

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Paul’s paper titled “Comparison of the polymorphs of VOPO4 as multi-electron cathodes for rechargeable alkali-ion batteries” has just been published in Journal of Materials Chemistry A. In collaboration with the Whittingham group, we performed a systematic first principles investigation, supported by careful electrochemical characterization and published experimental data, of the relative thermodynamic stability, voltage, band gap, and diffusion kinetics for alkali intercalation into the β, ε and αI polymorphs of VOPO4, a highly promising family of multi-electron cathodes.  We identify the β polymorph as the most promising for Li insertion, and the αI polymorph as  the most promising for Na insertion. We show that differences in the voltage, kinetics and rate capability of these different polymorphs for Li and Na insertion can be traced back to their fundamentally different VO6/VO5–PO4 frameworks.

Publications

Atomate

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Hanmei Tang and Iek-Heng Chu are co-authors on “Atomate: A High-Level Interface to Generate, Execute, and Analyze Computational Materials Science Workflows” just published in Computational Materials Science. This paper describes atomate, an open-source Python framework for computational materials science simulation, analysis, and design with an emphasis on automation and extensibility, that is built on top of pymatgen, FireWorks, and custodian. The Materials Virtual Lab are proud contributors to this great open science initiative! Check out the atomate package here.