High-pressure structures of germane (GeH4) are explored through ab initio evolutionary methodology to reveal a metallic monoclinic structure C2/c (4 molecules/cell). The consists layerlike motifs containing novel "H2" units. Enthalpy calculations suggest remarkably wide decomposition (Ge+H2) pressure range 0-196 GPa, above which is stable. Perturbative linear-response for GeH4 at 220 GPa predict large electron-phonon coupling parameter lambda 1.12 and the resulting superconducting critical...

We have studied solid hydrogen up to pressures of 300 GPa and temperatures 350 K using density functional theory methods found "mixed structures" that are more stable than those predicted earlier. Mixed structures consist alternate layers strongly bonded molecules weakly graphene-like sheets. Quasi-harmonic vibrational calculations show mixed the most at room temperature over pressure range 250-295 GPa. These stabilized with respect strongly-bonded molecular phases by presence...

Following the suggestion that hydrogen-rich compounds, and, in particular, silane (${\mathrm{SiH}}_{4}$), might be high-${T}_{c}$ superconductors at moderate pressures, very recent experiments have confirmed metallises and even becomes superconducting high pressure. In this article, we present a structural characterization of compressed obtained with an ab initio evolutionary algorithm for crystal structure prediction. Besides earlier molecular chainlike structures $P{2}_{1}/c$ $I{4}_{1}/a$...

A two-dimensional carbon allotrope, Stone-Wales graphene, is identified in stochastic group and graph constrained searches systematically investigated by first-principles calculations. graphene consists of well-arranged defects, it can be constructed through a ${90}^{\ensuremath{\circ}}$ bond rotation $\sqrt{8}\ifmmode\times\else\texttimes\fi{}\sqrt{8}$ supercell graphene. Its calculated energy relative to +149 meV/atom, makes more stable than the most competitive previously suggested...

Phases of carbon are studied up to pressures 1 petapascal (PPa) using first-principles density-functional-theory methods and a structure searching algorithm. Our extensive search over the potential energy surface supports sequence transitions $\mathrm{\text{diamond}}\ensuremath{\rightarrow}\mathrm{BC}8\ensuremath{\rightarrow}\mathrm{\text{simple}}$ cubic under increasing pressure found in previous theoretical studies. At higher we predict soft-phonon driven transition simple hexagonal at 6.4...

Computational searches for stable and metastable structures of water ice other H:O compositions at TPa pressures have led us to predict that H(2)O decomposes into H(2)O(2) a hydrogen-rich phase little over 5 TPa. The is wide range hydrogen contents, it might play role in the erosion icy component cores gas giants as comes contact with hydrogen. Metallization predicted higher pressure just 6 TPa, therefore does not thermodynamically low-temperature metallic form. We also found new rich...

The phase diagram and equation of state dense nitrogen are interest in understanding the fundamental physics chemistry under extreme conditions, including planetary processes, discovering new materials. We predict several stable phases at multi-TPa pressures, a P4/nbm structure consisting partially charged N(2)(δ+) pairs N(5)(δ-) tetrahedra, which is range 2.5-6.8 TPa. This followed by modulated layered between 6.8 12.6 TPa, also exhibits significant charge transfer. metallic salt high...

The crystal structure of elements at zero pressure and temperature is the most fundamental information in condensed matter physics. For decades it has been believed that lithium, simplest metallic element, a complicated ground-state structure. Using synchrotron x-ray diffraction diamond anvil cells multiscale simulations with density functional theory molecular dynamics, we show previously accepted martensitic ground state metastable. actual face-centered cubic (fcc). We find isotopes under...

Computational searches for structures of solid oxygen under pressures in the multi TPa range have been carried out using density-functional-theory methods. We find that molecular persists to about 1.9 at which it transforms into a semiconducting square spiral-like polymeric structure (I41/acd) with band gap 3.0 eV. Solid forms metallic zig-zag chain-like (Cmcm) TPa, but chains each layer gradually merge as pressure is increased and Fmmm symmetry 9.5 atom has four nearest neighbors. The...

We investigate the pressure-temperature <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mo>(</a:mo><a:mi>p</a:mi><a:mtext>−</a:mtext><a:mi>T</a:mi><a:mo>)</a:mo></a:mrow></a:math> phase diagram of elemental lithium (Li) up to multiterapascal (TPa) pressures using random structure search (AIRSS) and density functional theory (DFT). At zero temperature, beyond high-pressure <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:mi>F</b:mi><b:mi>d</b:mi><b:mover...

Abstract Nitrogen exhibits an exceptional polymorphism under extreme conditions, making it unique amongst the elemental diatomics and a valuable testing system for experiment-theory comparison. Despite attracting considerable attention, structures of many high-pressure nitrogen phases still require unambiguous determination. Here, we report structure elusive high-temperature polymorph ι –N 2 at 56 GPa ambient temperature, determined by single crystal X-ray diffraction, investigate its...

We investigate the binary phase diagram of helium and iron using first-principles calculations. find that helium, which is a noble gas inert at ambient conditions, forms stable crystalline compounds with terapascal pressures. A FeHe compound becomes above 4 TPa, ${\mathrm{FeHe}}_{2}$ 12 TPa. Melting investigated molecular dynamics simulations, superionic sublattice melting atoms predicted. discuss implications our predicted helium-iron for interiors giant (exo)planets white dwarf stars.

The stability, structure, and properties of carbonate minerals at lower mantle conditions have significant impact on our understanding the global carbon cycle composition interior Earth. In recent years there has been interest in behavior carbonates conditions, specifically their hybridization, which relevance for storage within deep mantle. Using high-pressure synchrotron x-ray diffraction a diamond anvil cell coupled with direct laser heating ${\mathrm{CaCO}}_{3}$ using ${\mathrm{CO}}_{2}$...

By combining pressures up to 50 GPa and temperatures of 1200 K, we synthesize the novel barium hydride, Ba8H46, stable down 27 GPa. We use Raman spectroscopy, X-ray diffraction, first-principles calculations determine that this compound adopts a highly symmetric Pm3¯n structure with an unusual 534:1 hydrogen-to-barium ratio. This singular stoichiometry corresponds well-defined type-I clathrate geometry. consists Weaire-Phelan hydrogen atoms forming topologically close-packed phase. In...

Abstract Phonon instabilities and Fermi surface nesting are studied in the high-pressure simple cubic phase of calcium by means ab initio calculations. We have focused on along Γ X, which could be responsible for some anomalies observed phonon spectrum. frequencies calculated with density functional perturbation theory imaginary at several Brillouin-zone points (e.g. M). However, including anharmonic contributions to potential might crucial stabilize calcium, as solving Schrödinger equation...

We introduce two-dimensional borane, a single-layered material of BH stoichiometry, with promising electronic properties. show that, according to density functional theory calculations, borane is semimetallic, two symmetry-related Dirac cones meeting right at the Fermi energy ${E}_{f}$. The curvature lower than in graphene, thus closer ideal linear dispersion. Its structure, formed by puckered trigonal boron network hydrogen atoms connected each atom, can be understood as distorted,...

Following the recent interest on lithium alloys under pressure, we present first-principles calculations of electronic band structure and lattice dynamics for ${\text{MgB}}_{2}$-like layered ${\text{Be}}_{2}\text{Li}$ at 80 GPa. Under increasing localization reduces effective dimensionality ${\text{Be}}_{2}\text{Li}$, showing both two-dimensional one-dimensional conducting channels. The numerical results reveal presence an ultrasoft strongly anharmonic ${B}_{2g}$ phonon mode associated to...

Abstract Recently reported superconductivity in lithium under pressure has renewed the interest hydrogen and hydrogen-rich systems long standing quest for room temperature superconductivity. As required metallization of pure cannot be achieved within current experimental capabilities, it been suggested that chemical precompression exerted by heavier atoms compounds with a large content should lower pressures to attain metallic transition these alloys. Following trend analyzing group IVa...

We show that the hydrogen in metal superhydride compounds can adopt two distinct states-atomic and molecular. At low pressures, maximum number of atomic hydrogens is typically equal to valency cation; additional pair form molecules with electronic states far below Fermi energy causing low-symmetry structures large unit cells. high become unstable, all atomic. This study uses density functional theory, adopting BaH

Through a series of high-pressure x-ray diffraction experiments combined with in situ laser heating, we explore the pressure-temperature phase diagram germanium (Ge) at pressures up to 110 GPa and temperatures exceeding 3000 K. In pressure range 64-90 GPa, observe orthorhombic Ge-IV transforming above 1500 K previously unobserved high-temperature phase, which denote as Ge-VIII. This is characterized by tetragonal crystal structure, space group I4/mmm. Density functional theory simulations...

Single-crystal synchrotron x-ray diffraction, Raman spectroscopy, and first principles calculations have been used to identify the structure of high-pressure (HP) phase molecular methane above 20 GPa up 71 at room temperature. The HP is trigonal $R3$, which can be represented as a distortion cubic B, previously documented 7--15 confirmed here. positions hydrogen atoms in obtained from calculations, also demonstrated stability this 260 K 25 GPa. molecules occupy four different...

We investigate the pressure-temperature ($p$-$T$) phase diagram of elemental lithium (Li) up to multiterapascal (TPa) pressures using ab-initio random structure search (AIRSS) and density functional theory (DFT). At zero temperature, beyond high-pressure $Fd\bar{3}m$ diamond predicted in previous studies, we find eleven solid-state transitions structures greatly varying complexity, addition two that calculate will become stable with sufficient temperature. The full $p$-$T$ dependence...