In a systematic investigation of scandium hydrides with high hydrogen content we predict seven phases of scandium hydrides (ScH4, ScH6, ScH7, ScH8, ScH9, ScH10, and ScH12), which are stable above 150 GPa. Zero point energies are essential in determining the phases and pressure ranges within which they are stable. The interconversion of the various hydrides is intriguing; in one case there is a “return” to a lower hydrogen content hydride with increasing pressure. We argue that these hydrides may be synthesized by compressing mixtures of ScH3 and H2 above 150 GPa. New H bonding motifs are uncovered, including “H5” pentagons or “H8” octagons in ScH9, ScH10, and ScH12. High T cs are predicted for ScH6, ScH7, ScH9, ScH10, and ScH12, with superconducting transition temperatures (T cs) of 120–169 K above 250 GPa, as estimated by the Allen–Dynes modified McMillan equation.

The computational and experimental exploration of the phase diagrams of binary hydrides under high pressure has uncovered phases with novel stoichiometries and structures, some which are superconducting at quite high temperatures. Herein we review the plethora of studies that have been undertaken in the last decade on the main group and transition metal hydrides, as well as a few of the rare earth hydrides at pressures attainable in diamond anvil cells. The aggregate of data shows that the propensity for superconductivity is dependent upon the species used to "dope" hydrogen, with some of the highest values obtained for elements that belong to the alkaline and rare earth, or the pnictogen and chalcogen families.

We report synchrotron X-ray diffraction, photoconductivity, and photoluminescence investigations of methylammonium-lead-bromide (MAPbBr) under various stress conditions, supported by density-functional-theory (DFT) calculations. The properties of MAPbBr show substantial dependence on the hydrostatic conditions. While nonhydrostatic compression of MAPbBr leads to amorphization above 2.4 GPa, under quasi-hydrostatic (Ar) and hydrostatic (He) pressure, the sample remains in crystalline phases. A sequence of phase transitions between two cubic phases and orthorhombic Pnma phase is observed when using Ar, or no pressure-transmitting-medium (PTM). In helium-PTM only transitions between the two cubic structures and a new isostructural phase transition with a large volume collapse to a third cubic-phase at 2.7 GPa was observed. The photoluminescence measurements indicate a pressure-induced band gap-narrowing in the cubic phase I, and a blue-shift in the orthorhombic structure. DFT calculations illustrate that the dynamics of the organic molecules and the inorganic lattice, coupled via the N-H···Br hydrogen-bonding interactions, affect the Pb-Br distance and the bandgap evolution under pressure.

Evolutionary algorithms and the particle swarm optimization method have been used to predict stable and metastable high hydrides of iron between 150-300 GPa that have not been discussed in previous studies. Cmca FeH 5 , P mma FeH 6 and P 2/c FeH 6 contain hydrogenic lattices that result from slight distortions of the previously predicted I4/mmm FeH 5 and Cmmm FeH 6 structures. Density functional theory calculations show that neither the I4/mmm nor the Cmca symmetry FeH 5 phases are superconducting. A P 1 symmetry FeH 7 phase, which is found to be dynamically stable at 200 and 300 GPa, adds another member to the set of predicted nonmetallic transition metal hydrides under pressure. Two metastable phases of FeH 8 are found, and the preferred structure at 300 GPa contains a unique 1-dimensional hydrogenic lattice.

First principles structural prediction and molecular dynamics (MD) calculations have been performed to examine the structures responsible for the recently reported metallic and superconducting phases of highly compressed CS2. The low pressure experimental molecular crystal structure was found to be metastable and transformed into a disordered structure above 10 GPa. At 60 GPa, the predicted low energy structures show molecular CS2 is separated into C and S dominant regions. A crystalline structure with the P21/m symmetry was found to be most stable from 60 to 120 GPa. The structure is formed from alternate layers of hexagonal C rings and S 2D-square-nets linked by C-S bonds. A non-crystalline structure with similar features structure is also predicted by MD calculations. Electron-phonon coupling calculations show this crystalline phase is superconductive. Contrary to the suggestions made from the experiments, no magnetism was found in all predicted low enthalpy high pressure structures. Moreover, the theoretical results do not support the proposal on the existence of hypervalent 6-coordinated carbon at 120 GPa.