arXiv subjects

Emily G. Ward

Publications and source records attributed to Emily G. Ward.

2 recordsLinked to original sources

arXiv2026

New Crystal Structures Hide in Plain Sight: A Stress Test for AI-Guided Materials Discovery

New types of crystal structures are discovered only rarely, and the artificial intelligence (AI) models now reshaping materials discovery have so far produced new chemical compositions within known structural families rather than genuinely new structures. We report GdNiSn4 and LuNiSn4, intermetallics that adopt a previously unreported structure type, found not by computation but by exploratory synthesis. Single-crystal diffraction shows that the structure is an intergrowth of two known structural units. We then use this system as a benchmark for two leading generative models, MatterGen and DiffCSP++. For DiffCSP++, the benchmark is performed in its crystallographically constrained setting, using the required space-group and Wyckoff-position inputs. Under our sampling budget, neither model recovers the experimentally reported monoclinic structure within the structural-matching tolerance. The generated structures are evaluated without further structural relaxation using the nonmagnetic analog LuNiSn4, where we rule out 4f magnetism as the cause. Because the new structure is built from familiar building blocks, it should be derivable. We argue that encoding chemical reasoning, such as the stacking of known motifs, is a concrete path toward AI that can discover structurally novel materials.

cond-mat.mtrl-sci↗

arXiv2024

Tight-Binding Models for Lone Pair, Heteroanionic Solids, and Application to Layered Oxyhalides

We provide a methodology to understand materials with complex bonding patterns, and apply it to the example of heteroanionic and lone pair materials. We build a tight-binding model based on Wannier functions fitted on density functional theory results, followed by enforcing symmetry on the atomic orbital basis set, and finally connecting and disconnecting sets of orbitals from the tight-binding model to understand their individual contribution to the resulting materials properties. We apply this methodology to complex materials, namely BiOCl and Bi$_2$YO$_4$Cl - part of a broader class of materials investigated for their applications in photocatalysis and photoluminescence. Our methodology can be generalized and applied to a wide variety of other materials, including halide perovskites, and multiferroic materials. This methodology allows us to isolate the origin of key electronic features in these materials, including the role of the Bi lone pair-anion bonding interaction - key to photoluminescence in many materials. Finally, we investigate the role of the crystal structure, Chlorine and Oxygen orbital energy levels and bonding in determining the photostability of bismuth oxyhalides. Our methodology allows us to understand the functionality of complex materials in an intuitive and qualitative manner.

cond-mat.mtrl-sci↗