A stable compound of helium and sodium at high pressure.

@article{Dong2017ASC,
  title={A stable compound of helium and sodium at high pressure.},
  author={Xiao Dong and Artem R. Oganov and Alexander F. Goncharov and Elissaios Stavrou and Sergey S. Lobanov and Gabriele Saleh and Guang-Rui Qian and Qiang Zhu and Carlo Gatti and Volker L. Deringer and Richard Dronskowski and Xiang-Feng Zhou and Vitali B. Prakapenka and Zuzana Kon{\^o}pkov{\'a} and Ivan A. Popov and Alexander I. Boldyrev and Hui-Tian Wang},
  journal={Nature chemistry},
  year={2017},
  volume={9 5},
  pages={
          440-445
        }
}
Helium is generally understood to be chemically inert and this is due to its extremely stable closed-shell electronic configuration, zero electron affinity and an unsurpassed ionization potential. It is not known to form thermodynamically stable compounds, except a few inclusion compounds. Here, using the ab initio evolutionary algorithm USPEX and subsequent high-pressure synthesis in a diamond anvil cell, we report the discovery of a thermodynamically stable compound of helium and sodium… 
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References

SHOWING 1-10 OF 63 REFERENCES
Pressure-induced bonding and compound formation in xenon-hydrogen solids.
TLDR
The formation of a stable compound in the Xe-H(2) binary system is described by a suite of X-ray diffraction and optical spectroscopy measurements, indicating a weakening of the intramolecular covalent bond as well as persistence of semiconducting behaviour in the compound to at least 255 GPa.
Stable structures of He and H 2 O at high pressure
The knowledge of the structures that can exist in compounds containing helium is of interest for understanding the conditions where and if this inert element can form structures where closed shell
High-pressure electrides: the chemical nature of interstitial quasiatoms.
TLDR
The computed Mg electride is used to understand metallic bonding in one class of electrides, and in general, the space confined between atoms in a high pressure environment offers up quantized states to electrons.
Stability of xenon oxides at high pressures.
TLDR
Using an ab initio evolutionary algorithm, the existence of thermodynamically stable Xe-O compounds at high pressures is predicted and calculations indicate large charge transfer in these oxides, suggesting that large electronegativity difference and high pressure are the key factors favouring the formation of xenon compounds.
Transparent dense sodium
TLDR
Experimental observations of a pressure-induced transformation of Na into an optically transparent phase at ∼200 GPa are reported, attributing the emergence of this dense insulating state not to atom pairing, but to p–d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices.
Anionic chemistry of noble gases: formation of Mg-NG (NG = Xe, Kr, Ar) compounds under pressure.
TLDR
It is demonstrated, using first-principles electronic structure calculations coupled to an efficient structure prediction method, that Xe, Kr, and Ar can form thermodynamically stable compounds with Mg at high pressure, suggesting that chemical species with a completely filled shell can gain electrons, filling their outermost shell(s).
Xenon Suboxides Stable under Pressure.
TLDR
It is found that the xenon suboxide Xe3O2 is the first compound to become more stable than the elements, at around P = 75 GPa, and an orthorhombic structure is suggested that comprises extended sheets of square-planar-coordinated xenon atoms connected through bent Xe-O-Xe linkages.
High pressure electrides: a predictive chemical and physical theory.
TLDR
By using a He lattice model to compress (with minimal orbital interaction at moderate pressures between the surrounding He and the contained atoms or molecules) atoms and an interstitial space, this work is able to semiquantitatively explain and predict the propensity of various elements to form HPEs.
The Properties of Hydrogen and Helium Under Extreme Conditions
Hydrogen and helium are the most abundant elements in the Universe. They are also, in principle, the most simple. Nonetheless, they display remarkable properties under extreme conditions of pressure
High pressure measurements of the He-Ne binary phase diagram at 296 K: Evidence for the stability of a stoichiometric Ne(He)2 solid.
The binary phase diagram of He-Ne mixtures has been measured at 296 K in a diamond anvil cell. It is of the eutectic type with no fluid-fluid separation of phases. A homogeneous solid mixture is
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