A little bit of lithium does a lot for hydrogen

Abstract

From detailed assessments of electronic structure, we find that a combination of significantly quantal elements, six of seven atoms being hydrogen, becomes a stable metal at a pressure approximately 1/4 of that required to metalize pure hydrogen itself. The system, LiH6 (and other LiHn), may well have extensions beyond the constituent lithium. These hypothetical materials demonstrate that nontraditional stoichiometries can considerably expand the view of chemical combination under moderate pressure.high pressure ͉ hydrogen metallization ͉ lithium chemistry T hree lines of thought-call them obsessions-impelled this investigation: (i) thinking of new pathways to promote and enhance the metallization of hydrogen, (ii) more generally the potential stability of new compounds with unusual stoichiometries under high pressures, and (iii) proposals for the design of new superconductors. As will be seen, we find two surprising ways (making good chemical sense) for the first, as well as sound theoretical evidence for the second. Based upon what is already known about possible superconductivity in metallic hydrogen, we find indications for the third.LiH, crystallizing in the NaCl structure with a band gap of 4.99 eV (1), is one stable point in the Li/H phase diagram, the only one other than the elements at ambient conditions. It remains stable at higher pressures; the reaction Li ϩ 1 2 H 2 3 LiH is computed to be exothermic at all of the pressures we have considered. Calculations predict that pressure-induced metallization and transformation to the CsCl structure occur simultaneously at approximately 329 GPa (2). The results of our density functional theory (DFT) calculations on LiH are given in the supporting information (SI).Hydrogen also vehemently resists metallization.

Theoretical study of the ground-state structures and properties of niobium hydrides under pressure

“…The situation thus differs markedly from LiH n , 2 and also from CaH n 5 where for certain stoichiometries one clearly finds paired hydrogens. There is a definite connection to the CaH 6 structure at 150 GPa, 5 which features an extended H network, albeit different from the ones we find here.…”

“…In equation (2), N f is the electronic density of electron states at the Fermi level. The linewidth γ q j of a phonon mode j at wave vector q, arising from EPC is given by…”

High-pressure crystal structures and superconductivity of Stannane (SnH 4 )

“…We propose to call these chemically active H 2 units perhydride groups; they have so far not been observed at ambient conditions, but predicted to exist at high pressures in GeH 4 (ref. 17) and unique lithium hydrides LiH 2 , LiH 6 and LiH 8 (39). Perhydride groups were also predicted in the structures of SnH 4 calculated in refs.…”

Superconductive sodalite-like clathrate calcium hydride at high pressures

“…Introduction of an electronegative element, as was demonstrated in the case of K-Ag (16), increases the ability of the electronegative Ag atoms to accommodate electrons from K into the outermost 5s and 5p valence shells, thereby forming a bonding network and stabilizing the alloy structures that otherwise would not be observed under ambient pressures. Recently, Zurek et al (17,18) demonstrated that charge transfer from lithium or sodium to hydrogen molecules under high pressures could lead to the formation of new metallic lithium-or sodium-hydride alloys. Depending on the stoichiometry, the structures consist of "predissociated" molecular H 2 and/or monoatomic hydrogen.…”