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Metal superhydrides, known for their high hydrogen content and polyhedral hydrogen cages, are promising candidates for high-temperature superconductivity. Despite extensive studies on binary metal superhydrides, there remains a large, unexplored chemical space, particularly regarding non-integer hydrogen-to-metal ratios. By integrating the "chemical template effect" with machine learning algorithms, we developed a specialized structure discovery workflow that significantly enhances the efficiency of predicting stable superhydrides. Within the compiled dataset used in this work, our method led to the identification of 13 new structural prototypes and 31 stable metal superhydrides, representing a 23% increase in discoveries. The 3D hydrogen clathrates in these compounds are significantly correlated with high superconducting transition temperatures (Tc), and our approach achieves a remarkable 65% increase. Most of these structures contain over 50 atoms per primitive cell, with the I4/m M10H84 prototype having the largest unit cell, containing 94 atoms. Additionally, 19 of the newly identified superhydrides exhibit Tc > 100 K, highlighting the potential for higher Tc materials within the 3D hydrogen clathrate structures. The method also shows good potential to search for ternary superhydrides on a large scale. 

Numerous experimental and theoretical studies showed that alkali and alkaline metals transform into various structures with large open interstitials under pressure, an intricate behavior that is caused by the electron transfer among s, p, and d atomic and quasi-atomic orbitals. However, little is known about the behavior of these metals beyond this pressure region. Using first-principles calculations and crystal structure search methods, we show that Cs returns to simple close-packed structures under ultrahigh pressure, including the transition from DHCP to FCC structure at 183 GPa and a further transition into HCP at 655 GPa. More significantly, under ultra-high pressure, the 5p electrons are activated and form strong chemical bonds between neighboring Cs atoms that govern the properties of Cs under very high pressure, including the transition from FCC to HCP. 

Electrides have emerged as promising materials with exotic properties due to the presence of localized electrons detached from all atoms. Despite the continuous discovery of many new electrides, most of them are based on atypical compositions, and their applications require an inert surface structure to passivate reactive excess electrons. Here, we demonstrate a different route to attain tunable electrides. We first report that monolayer transition metal dichalcogenides (TMDCs) exhibit weak electride characteristics, which is the remainder of the electride feature of the transition metal sublattice. By introducing chalcogen vacancies, the enhanced electride characteristics are comparable to those of known electrides. Since the precise tailoring of the chalcogen vacancy concentration has been achieved experimentally, we proposed that TMDCs can be used to build electrides with controllable intensities. Furthermore, we demonstrate that the electride states at the chalcogen vacancy of monolayer TMDCs will play an important role in catalyzing hydrogen evolution reactions. 

Most metals adopt simple structures such as body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP) structures in specific groupings across the periodic table, and many undergo transitions to surprisingly complex structures on compression, not expected from conventional free-electron-based theories of metals. First-principles calculations have been able to reproduce many observed structures and transitions, but a unified, predictive theory that underlies this behavior is not yet in hand. Discovered by analyzing the electronic properties of metals in various lattices over a broad range of sizes and geometries, a remarkably simple theory shows that the stability of metal structures is governed by electrons occupying local interstitial orbitals and their strong chemical interactions. The theory provides a basis for understanding and predicting structures in solid compounds and alloys over a broad range of conditions.