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Violation of the Minimum H-H Separation "Rule" for Metal Hydrides

P. Ravindran·P. Vajeeston·R. Vidya·A. Kjekshus·H. Fjellvaag
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Abstract

Using gradient-corrected, all-electron, full-potential, density-functional calculations, including structural relaxations, it is found that the metal hydrides $RT$InH$_{1.333}$ (R = La, Ce, Pr, or Nd; T = Ni, Pd, or Pt) possess unusually short H-H separations. The most extreme value (1.454 Å) ever obtained for metal hydrides occurs for LaPtInH$_{1.333}$. This finding violates the empirical rule for metal hydrides, which states that the minimum H-H separation is 2 Å. Electronic structure, charge density, charge transfer, and electron localization function analyses on $RT$InH$_{1.333}$ show dominant metallic bonding with a non-negligible ionic component between T and H, the H-H interaction beingweakly metallic. The paired, localized, and bosonic nature of the electron distribution at the H siteare polarized towards La and In which reduces the repulsive interaction between negatively charged H atoms. This could explain the unusually short H-H separation in these materials. Also, R-R interactions contribute to shielding of the repulsive interactions between the H atoms.

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P. Ravindran, P. Vajeeston, R. Vidya, A. Kjekshus, H. Fjellvaag. 2002-09-13. Violation of the Minimum H-H Separation "Rule" for Metal Hydrides. https://doi.org/10.1103/physrevlett.89.106403

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