Prediction of Stable Ground-State Lithium Polyhydrides under High Pressures.
Hydrogen-rich compounds are important for understanding the dissociation of dense molecular hydrogen, as well as searching for room temperature Bardeen-Cooper-Schrieffer (BCS) superconductors. A recent high pressure experiment reported the successful synthesis of novel insulating lithium polyhydrides above 130 GPa. However, the results are in sharp contrast to a previous theoretical prediction by the PBE functional that around this pressure range all lithium polyhydrides (LiHn(n = 2-8)) should be metallic. In order to address this discrepancy, we perform an unbiased structure search with first-principles calculation by including the van der Waals interaction that was ignored in the previous prediction to predict the high pressure stable structures of LiHn(n = 2-11, 13) up to 200 GPa. We reproduce the previously predicted structures, and further find novel compositions that adopt more stable structures. The van der Waals functional (vdW-DF) significantly alters the relative stability of lithium polyhydrides, and predicts that the stable stoichiometries for the ground state should be LiH2and LiH9at 130-170 GPa, and LiH2, LiH8, and LiH10at 180-200 GPa. Accurate electronic structure calculation with GW approximation indicates that LiH, LiH2, LiH7, and LiH9are insulative up to at least 208 GPa, and all other lithium polyhydrides are metallic. The calculated vibron frequencies of these insulating phases are also in accordance with the experimental infrared (IR) data. This reconciliation with the experimental observation suggests that LiH2, LiH7, and LiH9are the possible candidates for lithium polyhydrides synthesized in that experiment. Our results reinstate the credibility of density functional theory in the description of H-rich compounds, and demonstrate the importance of considering van der Waals interaction in this class of materials.
National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, CAEP , P.O. Box 919-102, Mianyang, Sichuan People's Republic of China , 621900.|Institute of Atomic and Molecular Physics, College of Physical Science and Technology, Sichuan University , Chengdu, Sichuan People's Republic of China , 610065.
Yangmei
http://orcid.org/0000-0002-2182-2842
Y
Chen
National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, CAEP , P.O. Box 919-102, Mianyang, Sichuan People's Republic of China , 621900.
Hua Y
http://orcid.org/0000-0001-5757-3027
HY
Geng
National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, CAEP , P.O. Box 919-102, Mianyang, Sichuan People's Republic of China , 621900.|Institute of Atomic and Molecular Physics, College of Physical Science and Technology, Sichuan University , Chengdu, Sichuan People's Republic of China , 610065.|School of Science, Jiangxi University of Science and Technology , Ganzhou, Jiangxi People's Republic of China , 341000.
Xiaozhen
X
Yan
National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, CAEP , P.O. Box 919-102, Mianyang, Sichuan People's Republic of China , 621900.
Yi
Y
Sun
National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, CAEP , P.O. Box 919-102, Mianyang, Sichuan People's Republic of China , 621900.
Qiang
Q
Wu
Institute of Atomic and Molecular Physics, College of Physical Science and Technology, Sichuan University , Chengdu, Sichuan People's Republic of China , 610065.
Xiangrong
X
Chen