Efficient autonomous material search method combining <i>ab</i> initio calculations, autoencoder, and multi-objective Bayesian optimization

Autonomous material search systems that combine ab initio calculations and Bayesian optimization are very promising for exploring huge material spaces. Setting up an appropriate material search space is necessary for efficient autonomous material search. However, performing the autonomous search within the material space set up using the prepared descriptors is not sufficient to obtain an efficient search, which can be achieved by prioritizing specific descriptors and properties. Here, a material search system that can autonomously search the huge material space while performing multi-objective optimization that considers similarities among elements and emphasizes specific descriptors is proposed. This system has been used for a material exploration of Heusler alloys. The system has successfully proposed several candidate materials with half-metallic properties. The proposed system is very versatile and can be applied to various properties and material systems.</p

Quasi-Periodic Growth of One-Dimensional Copper Boride on Cu(110)

An unexplored material of copper boride has been realized recently in two-dimensional form at a (111) surface of the fcc copper crystal. Here, one-dimensional (1-D) boron growth was observed on the Cu(110) surface, as probed by atomically resolved scanning probe microscopy. The 1-D copper boride was composed of quasi-periodic atomic chains periodically aligned parallel to each other, as confirmed by Fourier transform analysis. The 1-D growth unexpectedly proceeded across surface steps in a self-assembled manner and extended over several 100 nm. The long-range formation of a 1-D quasi-periodic structure on a surface has been theoretically modeled as a 1-D quasi-crystal and the predicted conditions matched the structural parameters obtained by the experimental work here. The quasi-periodic 1-D copper boride system enabled a way to examine 1-D quasi-crystallinity on an actual material