Non-equilibrium molecular dynamics simulations were conducted to study the growth and dissolution of a spherical methane hydrate crystallite, using a polarizable water potential, encircled by a liquid phase of saturated water and methane, both in the microwave to far-infrared range and under applied external electromagnetic (e/m) fields (5 GHz to 7.5 THz) at r.m.s.electric-field strengths of up to the order of 1 V$\cdot$nm$^{-1}$ — in an attempt to assess and model the "threshold" field intensities required to initiate hydrate dissolution. The average growth rate of the crystallite in the absence of a field was found to be approximately 0.32 water and 0.045 methane molecules per picosecond. Upon applying e/m fields, deviations from zero-field crystal growth patterns were observed for r.m.s. field strengths, especially at $\sim 1$ V$\cdot$nm$^{-1}$ as a rough `threshold'. When the water dipole was aligned with the external field, systematic frequency variations were observed, providing a mechanistic rationale for field-coupling effects on dipole direction/magnitude and hydrogen-bonding shifts.

Compressed calcium undergoes successive structural transitions under high pressure. In this study, high-pressure polymorphs of elemental calcium were investigated using a machine-learned interatomic potential combined with a sensible random structure search. Two new energetically favourable and dynamically stable phases were predicted, crystallizing in the $P$-$42_{1}c$ and $P$-$31c$ space groups at high pressure. Both structures are predicted to be metallic and likely exhibit phonon-mediated superconductivity. Using the Allen-Dynes modified McMillan equation, the superconducting critical temperatures ($T_{\rm c}$) were estimated to be 26 K for the $P$-$42_{1}c$ phase at 200 GPa and 31 K for the $P$-$31c$ phase at 250 GPa, which are comparable to the highest experimentally observed $T_{\rm c}$ for calcium (29 K at 216 GPa). These relatively high $T_{\rm c}$ values are attributed to strong electron-phonon coupling between partially occupied d states and moderate-frequency phonon modes. These findings provide further insight into the complex polymorphism and superconductivity of elemental calcium under extreme conditions.

The recent synthesis of the superhydride LaB$_{2}$H$_{8}$, which exhibits a superconducting transition temperature ($T_{\rm c}$) of 106 K at 90 GPa, offers a promising avenue for exploring high-temperature superconductivity. However, the underlying superconducting mechanism remains elusive. Here, we employ first-principles calculations to systematically investigate the electronic structure, lattice dynamics, electron-phonon coupling, and molecular-orbital features of LaB$_{2}$H$_{8}$. Our analysis reveals that the structural stability and metallic conductivity primarily originate from the covalent B-H bonds within the B$_{2}$H$_{8}$ units. Furthermore, we observe a pronounced softening of low-frequency phonons at elevated pressures, which induces strong electron-phonon coupling and serves as the key driving force for superconductivity in this system. This work not only elucidates the superconducting mechanism in LaB$_{2}$H$_{8}$ but also highlights the importance of covalent hydrogen-based motifs in designing new high-$T_{\rm c}$ superconductors.

Titanium-boron (Ti-B) compounds exhibit great promise as superhard materials due to titanium's low atomic mass and abundant valence electrons. In this work, we systematically investigated the crystal structures of TiB$_{6}$ under pressures ranging from 0-100 GPa using the CALYPSO algorithm combined with first-principles calculations. Phonon dispersion analysis and elastic-constant evaluations confirm the dynamic and mechanical stability of five predicted TiB$_{6}$ structures. Notably, the $\alpha $-Amm2-TiB$_{6}$ structure was predicted to have a remarkable Vickers hardness of 56 GPa, as estimated by Chen's empirical model. All five structures are thermodynamically stable under ambient conditions, suggesting viable synthetic pathways. Their outstanding bulk moduli and ultrahigh hardness further classify them as potential incompressible and superhard materials. These theoretical insights lay a robust foundation for future experimental synthesis efforts.

The pressure-induced structural transformation in metallic glass (MG) is a challenging and important subject in condensed matter physics. In the present first-principles molecular dynamics study, the atomic packing of La$_{75}$Al$_{25}$ MG under pressure was investigated, and the structure was predicted to crystallize at 92 GPa. It is found that the distributions of La and Al atoms are not homogeneous, as often assumed. In particular, Al atoms form aggregates in the glass structure, exhibiting strong covalent characteristics of the Al-Al bonds. The pressure-induced crystallization is not only caused by the dominant packing of the larger La atoms but is also facilitated by the presence of these rigid Al clusters.

In alkali silicate glasses with $\le 50$ mol%$M_{2}$O ($M={\rm Na}$, K, Rb, Cs), the existence of $>1$ mol%reactive "free" oxide (FO, where O is not bonded to Si) has been a highly controversial topic over the past 15 years. Unlike their crystalline analogues, Raman and $^{29}$Si nuclear magnetic resonance (NMR) studies since 1980 have shown that two or more $Q^{n}$ ($n=$0-4) species are present in silicate glasses over a wide range of compositions. For example, $M_{2}$SiO$_{3}$ crystals contain only $Q^{2}$ species; however, glasses of the same composition exhibit $Q^{1}$ and $Q^{3}$ in addition to $Q^{2}$. Previous Raman and NMR studies on alkali silicate glasses have related the abundances of these three species solely through disproportionation reactions (e.g. $2{ Q}^{2}\Leftrightarrow { Q}^{1}+{ Q}^{3}$). In doing so, polymerization reactions (e.g. $2{ Q}^{2}\Leftrightarrow 2{ Q}^{3}+{\rm FO}$) were completely neglected. By combining published O 1s x-ray photoelectron spectroscopy (XPS) spectra, $^{29}$Si NMR and Raman results for 40 mol%and 50 mol%Na$_{2}$O, K$_{2}$O, and BaO glasses, together with new molecular dynamics (MD) simulations of Na$_{4}$SiO$_{4}$ glass, we provide consistent and compelling evidence for the existence of $>1$ mol%FO in these glasses and melts. In particular, for 50 mol%K$_{2}$O silicate glass, all three experimental techniques estimate FO to be $\ge 7$ mol%, while MD simulations of Na$_{4}$SiO$_{4}$ yield $\sim 5$ mol%FO. Our analysis requires revised assignments (challenging decades of "conventional wisdom") for $^{29}$Si NMR and Raman spectra, based on O mass balance, recognition of M-BO bonding effects first identified in O 1s XPS spectra, and quantitative analysis of Raman spectra for 40-50 mol%Na$_{2}$O, K$_{2}$O, and BaO glasses. These FO values are comparable to those now accepted for alkaline-earth silicate glasses. The importance of this reactive FO for chemical reactivity (e.g. with H$_{2}$O and CO$_{2}$), bioactivity, and physical properties (e.g. melting) of silicate glasses is discussed.

Nickel-based bimetallic alloys are considered thermally and structurally stable, while also possessing desirable catalytic and magnetic functionalities and being highly abundant and affordable. The electronic structure of such alloys is of particular interest from the perspective of atomic size mismatch and elemental crystal structure compatibility. In this study, we utilize x-ray techniques, including x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), and x-ray photoelectron spectroscopy (XPS), to understand the strain and ligand effects on charge redistribution upon alloying. We investigate the elemental crystal structures for incompatible alloys of Ni (fcc) and Fe (bcc), and the compatible crystal structure of Ni (fcc) and Cu (fcc) for comparison. Emphasis is placed on interpreting the metal 2p XPS binding energy shift in binary alloys, where one element is diluted into the other, based on the framework of strain and ligand effects and the charge compensation model of Watson et al. Of interest are the different "compressibilities" of the 4s and 3d wavefunctions within the Wigner-Seitz volume, $V_{\rm WS}$, and the volume-strain effect resulting in intra-atomic 4s-3d rehybridizations within the alloy, as well as the chemical intuition of charge transfer based on the ligand effect (electronegativity). These considerations provide perspective on "internal pressure" due to the strain effect and help in understanding the x-ray data and their correlation with the electronic structures and properties of bimetallic alloy systems.

Electrides, characterized by interstitial quasi-atoms (ISQs) where electrons occupy lattice voids instead of atomic orbitals, provide a unique platform for discovering novel superconductors and mixed-conduction materials. Here, using crystal structure prediction combined with first-principles calculations, we systematically explore lithium-rich Li-Bi compounds under high pressure. Several new Li-rich stoichiometries, LiBi, Li$_{11}$Bi$_{2}$, Li$_{9}$Bi, and Li$_{10}$Bi, are identified as thermodynamically stable. Among them, the $C$2$/m$ phase of Li$_{10}$Bi features one-dimensional ISQ networks, exhibiting both metallic and electride characteristics. Electron-phonon coupling analysis reveals a dome-shaped evolution of superconducting transition temperature ($T_{\rm c}$), reaching a maximum value of 9.9 K at 35 GPa, where the superconductivity is primarily driven by strong Li-derived phonon modes. Ab initio molecular dynamics simulations further reveal a temperature-induced superionic transition above 700 K, where Li$^{+}$ ions diffuse freely while Bi atoms remain fixed within the lattice. This coexistence of superconductivity and superionicity within a single crystalline framework highlights Li$_{10}$Bi as a prototype dual-functional electride, bridging the gap between quantum superconductors and solid-state lithium-ion conductors. These findings open a new route for designing multifunctional materials that integrate electronic and ionic transport for next-generation energy and quantum applications.

Ternary metal hydrides play a vital role in the search for conventional high-temperature superconductors under near-ambient pressures. In this study, we examine the dynamic, mechanical, and electronic properties of the C15-type ZrCr$_{2}$H$_{x}$ ($0 < x \le 4$) compounds at 0-20 GPa using first-principles simulations. We find that protons diffuse predominantly via the interstitial network composed of $g$ and $e$ sites, avoiding high-barrier $b$ sites. Proton diffusion is insignificant at 300 K, but increases markedly with increasing temperature, leading to superionic transitions at 900 K in all these hydrides. Diffusion enhances the occupation probability of neighboring interstitial sites, resulting in short H-H separations that violate the Switendick criterion. The calculated thermoelastic properties indicate mechanical stability of ZrCr$_{2}$H$_{x}$ at room temperature. In ZrCr$_{2}$H$_{4}$, the high hydrogen concentration leads to a clear contribution of H $s$ orbitals to metallicity, suggesting that C15-type intermetallic hydrides have great potential to form high-temperature superconductors at low pressures.

The CuBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{10+\delta}$ (Cu1234) superconductor exhibits a unique combination of high critical temperature (118 K ambient $T_{\rm c}$), high critical current density ($J_{\rm c}$), and high irreversibility field ($H_{\rm irr}$), i.e., the so-called triple-high attributes, making it a promising candidate for high-temperature and high-field applications. However, the growth of high-quality single crystals has been hindered by contamination from traditional sample capsules used in conventional high-pressure synthesis, leading to suppressed $T_{\rm c}$. In this work, we develop a modified high-pressure sample assembly utilizing a capsule with MgO as the inner layer and Pt as the outer layer, which effectively prevents undesirable doping of Pt into Cu1234 that suppresses $T_{\rm c}$. This approach enables the successful growth of Cu1234 single crystals with a sharp superconducting transition at $T_{\rm c} \sim 115$ K, comparable to that of polycrystalline samples. Structural and compositional analyses confirm the phase purity, strong $c$-axis orientation, and near-ideal stoichiometry close to the Cu1234 formula. These high-quality Cu1234 single crystals provide a reliable platform for elucidating the intrinsic mechanisms of the exceptional triple-high superconducting properties of the Cu1234 system.