Polyhydrides of the Alkaline Earth Metals: A Look at the Extremes under Pressure

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• 作者：James Hooper ; Bahadir Altintas ; Andrew Shamp ; Eva Zurek
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：February 14, 2013
• 年：2013
• 卷：117
• 期：6
• 页码：2982-2992
• 全文大小：668K
• 年卷期：v.117,no.6(February 14, 2013)
• ISSN：1932-7455

文摘

Evolutionary structure searches are coupled with density functional theory calculations to predict the most stable stoichiometries and structures of beryllium and barium polyhydrides, MH_n with n > 2 and M = Be/Ba, under pressure. Even though the BeH_n stoichiometries we explored do not become thermodynamically stable with respect to decomposition into the classic hydride BeH₂ and H₂ up to 200 GPa, we find a new phase of BeH₂ with R3̅m symmetry above 150 GPa. The barium polyhydrides become thermodynamically preferred by 20 GPa. They sport complex hydrogenic sublattices composed of H^{鈥?/sup>, H₃鈥?/sup>, and H₂ units. BaH₆ is the first stoichiometry to emerge as stable and metallic (60 GPa using the Perdew鈥揃urke鈥揈rnzerhof functional), and the P4/mmm symmetry structure is estimated to become superconducting below 30鈥?8 K at 100 GPa. Phases with an even greater hydrogen content lie on the convex hull at higher pressures, and an intriguing BaH₁₀ stoichiometery becomes the global thermodynamic minimum around 150 GPa. BaH₁₀ remains metallic over its predicted domain of existence, and its Ba鈥揃a distances resemble those found in the complex Ba鈥揑Vc structure at 19 GPa.}