DIRECT Sampling for Robust MLPs

Ji’s work on “Robust training of machine learning interatomic potentials with dimensionality reduction and stratified sampling” is now out in npj Computational Materials! Machine learning interatomic potentials (MLIPs) enable accurate simulations of materials at scales beyond that accessible by ab initio methods. In this work, we present DImensionality-Reduced Encoded Clusters with sTratified (DIRECT) sampling as an approach to select a robust training set of structures from a large and complex configuration space. By applying DIRECT sampling on the Materials Project relaxation trajectories dataset with over one million structures and 89 elements, we develop an improved materials 3-body graph network (M3GNet) universal potential that extrapolates more reliably to unseen structures. We further show that molecular dynamics (MD) simulations with the M3GNet universal potential can be used instead of expensive ab initio MD to rapidly create a large configuration space for target systems. We combined this scheme with DIRECT sampling to develop a reliable moment tensor potential for titanium hydrides without the need for iterative augmentation of training structures.

Check out this work here. If you want to use DIRECT sampling for your work, please check out our implementation available on our MAML repository on Github.

MRS Fall 2023 Tutorial on ML for SSBs

Ji Qi gave a tutorial talk on “Machine Learning and High-Throughput Discovery and Design of Next Generation Electrode and Superionic Materials and Their Interfaces for SSBs” at the MRS Fall 2023! This tutorial provides an overview of how our group is using ML techniques to gain insights and discovery alkali superionic conductors, as well as the many open-source software packages that we have developed for these purposes. A recording of this talk is available on our group’s YouTube channel (and embedded above).

Li diffusivity at the grain boundaries

Randy’s work on “Lithium dynamics at grain boundaries of β-Li3PS4 solid electrolyte” has just been published in Energy Advances! Randy was a visiting scientist in the Materials Virtual Lab from NIMS Japan in 2021-2023.

Lithium diffusivity at the grain boundaries of solid electrolytes (SEs) can strongly impact the final performance of all-solid-state Li ion batteries (SSLBs). In this study, we systematically investigate the Li ion transport in tilt and twist GBs as well as amorphous/crystal interfaces of β-Li3PS4 by performing large-scale molecular dynamics (MD) simulations with a highly accurate moment tensor interatomic potential (MTP). We find that the Li ion conductivities at the GBs and amorphous/crystal interfaces are 1–2 orders of magnitude higher than that in the bulk crystal. The Li pathway network in twist GBs and amorphous/crystal interfaces comprises persisting large Li ring sub-networks that closely resemble those found in the bulk amorphous structure, whereas more smaller and short-lived Li ring sub-networks are detected in tilt GBs and the bulk crystal. The concentration of persisting large Li ring sub-networks in the GB and amorphous/crystal interfaces is directly proportional to the degree of Li site disordering which in turn correlates with GB conductivity. Our findings provide useful insights that can guide the optimization of conductivity not only in β-LPS but also in other sulfide-type solid electrolytes through possible GB engineering.

Check out the work here.

NUS Seminar Talk on “Universal Machine Learning Models for Unconstrained Materials Design”

Prof Ong gave an invited seminar talk at the National University of Singapore on Jul 5 2023. In this talk, Prof Ong discusses the different ways in which machine learning (ML) can be used to improve or accelerate the various steps of in silico materials design. The general goal is to preserve the universality and accuracy of ab initio approaches as far as possible while achieving orders of magnitude speed-ups and improved scaling. Prof Ong shared his view that graph deep learning models trained on large diverse materials datasets, such as the M3GNet universal potential, are the “foundation” models for materials science. He further argues that the most robust approach is to replace the smallest, most expensive step in the materials design workflow with ML and preserve as much as the physics of thermodynamics, kinetics, etc. in the computation of materials properties.

Compositionally complex perovskite solid electrolytes


The Materials Virtual Lab is proud to be part of a collaborative work titled “Compositionally complex perovskite oxides: Discovering a new class of solid electrolytes with interface-enabled conductivity improvements” recently published in Cell Press Matter! This work was performed under the Materials Research Science and Engineering Center (MRSEC) at UC Irvine together with the groups of Prof Xiaoqing Pan @ UCI and Prof Jian Luo @ UCSD.

Compositionally complex ceramics (CCCs), including high-entropy ceramics, offer a vast, unexplored compositional space for materials discovery. Here, we propose non-equimolar compositionally complex perovskite oxide (CCPO) solid electrolytes with improved lithium ionic conductivities beyond the limit of conventional doping. For example, we demonstrate that the ionic conductivity can be improved by >60% in (Li0.375Sr0.4375)(Ta0.375Nb0.375Zr0.125Hf0.125)O3-d. MAVRL group member, Ji Qi, developed a machine learning interatomic potential (MLIP) for this 7-component CCPO using an active learning protocol, and demonstrated this enhanced ionic conductivity can be attributed to enhanced GB diffusitivity that is related to the absence of Li depletion at GB regions, which is observed in the resistive GB of the LLTO. This work suggests new routes for discovering and tailoring CCCs for energy storage and many other applications.

Check out this work here.

Materials Graph Library

We are excited to announce that Materials Graph Library (matgl), our Deep Graph Library/PyTorch reimplementation of the MatErials Graph Network (MEGNet) and Materials 3-body Graph Network (M3GNet) models, is now ready for widespread beta testing! We finally achieved near-feature parity with the original implementations in Tensorflow after months of hard work. The new MatGL includes retrained models of the M3GNet universal potential and the MEGNet formation energy and multi-fidelity band gap models. We have also taken the trouble to include example notebooks to get users started quickly. We believe this new implementation will be more future-proof and extensible. Feedback/issue reports are definitely welcome.

This is a collaborative effort between the Materials Virtual Lab and Intel Labs.

243rd ECS Meeting Presentation on Machine Learning for Solid State Batteries: Progress vs Hype

Prof Shyue Ping Ong gave a talk at the 243rd Electrochemical Society (ECS) Meeting in Boston on May 30 2003 on “Machine Learning for Solid State Batteries: Progress vs Hype:. Machine learning in materials science and solid-state batteries are two topics that have captured the imagination of researchers in recent years. Therefore, it is unsurprising that many researchers have attempted to apply the advances in ML to the discovery and study of materials for solid-state batteries. In this talk, Prof Ong discusses the importance of going back to fundamentals in the application of ML to materials for solid-state batteries. I will highlight areas where ML has had a transformative impact on our understanding and discovery of solid electrolytes, and what are some of the remaining challenges that remain to be surmounted.

Multi-scale investigation of MoNbTi and TaNbTi MPEAs

Hui’s swansong collaborative work on “Multi-scale investigation of short-range order and dislocation glide in MoNbTi and TaNbTi multi-principal element alloys” is now out in npj Computational Materials! This is a really exciting work that showcases an electron (DFT) to atom (machine learning interatomic potentials) to continuum (phase field dislocation dynamics) approach to the study of materials. It is a collaborative work between Hui and Lauren Fey of the group of Irene Beyerlein at UC Santa Barbara.

Refractory multi-principal element alloys (RMPEAs) are promising materials for high-temperature structural applications. In this work, we performed an electron-to-atom-to-continuum study of the role of short-range ordering (SRO) on dislocation glide in the MoNbTi and TaNbTi RMPEAs. Monte carlo/molecular dynamics simulations with a moment tensor potential show that MoNbTi exhibits a much greater degree of SRO than TaNbTi and the local composition has a direct effect on the unstable stacking fault energies (USFEs). From mesoscale phase-field dislocation dynamics simulations, we find that increasing SRO leads to higher mean USFEs and stress required for dislocation glide. The gliding dislocations experience significant hardening due to pinning and depinning caused by random compositional fluctuations, with higher SRO decreasing the degree of USFE dispersion and hence, amount of hardening. Finally, we show how the morphology of an expanding dislocation loop is affected by the applied stress.

Check out the work here.

Why software development is important

Jean Fan’s recent column in Nature on “Why it’s worth making computational methods easy to use” is an excellent article on a topic close to my heart. The following quote rings especially true.

“We probably spent as many hours making STdeconvolve accessible as we did in developing it. Some of my colleagues have been surprised by this effort, as those hours won’t lead to new publications.”

Our group is the maintainer of pymatgen, maml, matgl and a few other software used extensively by the materials science community. Colleagues frequently asked me the same question – “Why do I do it? Surely a professor can spend the time writing proposals, papers, etc.?” I disagree. Our group’s code is a critical avenue in which we contribute and engage with the community. A well written and maintained code can probably 10-100x the impact of a work beyond that one publication. I argue the Materials Virtual Lab, in open collaboration with thousands of other researchers, have saved millions of hours in research hours because some graduate student or postdoc was able to do their research faster and more accurately. That may not appear in my CV, but it makes me motivated to continue to do what I do. – Shyue

GB resistance in oxide solid electrolytes

Ji Qi’s co-first author paper on “Atomic-scale origin of the low grain-boundary resistance in perovskite solid electrolyte Li0.375Sr0.4375Ta0.75Zr0.25O3 (LSTZ0.75)” has been published in Nature Communications! This is a highly-collaborative work under the Center for Complex and Active Materials (CCAM), an NSF MRSEC. Perovskite solid electrolytes for all-solid-state lithium-ion batteries are often plagued by grain boundary (GB) resistance. In this work, the CCAM team use aberration-corrected scanning transmission electron microscopy and spectroscopy, along with an active learning moment tensor potential, to reveal the
atomic scale structure and composition of LSTZ0.75 grain boundaries. A key finding is that Li depletion in the GB is mitigated in LSTZ0.75 compared to the typical LLTO peroskite SE. Instead, a nanoscale defective cubic perovskite interfacial structure that contained
abundant vacancies is formed.

Ji’s contribution is the development of an accurate machine learning interatomic potential to study the highly complex LLTO and LSTZ perovskites, including the GB structures. Using MC and MC simulations, we demonstrate that Li enrichment and Sr vacancies in the GBs of LSTZ play a key role in fast diffusion in LSTZ.

Check out this work here.