Thermodynamic stability of alkali-metal--zinc double-cation borohydrides at low temperatures

Thermodynamic stability of alkali-metal–zinc double-cation borohydrides at low temperatures

Tran Doan Huan, Maximilian Amsler, Riccardo Sabatini, Vu Ngoc Tuoc, Nam Ba Le, Lilia M. Woods, Nicola Marzari, and Stefan Goedecker

Phys. Rev. B 88, 024108 – Published 12 July 2013

Abstract

We study the thermodynamic stability at low temperatures of a series of alkali-metal–zinc double-cation borohydrides, including LiZn(BH $_{4}$ ) $_{3}$ , LiZn $_{2}$ (BH $_{4}$ ) $_{5}$ , NaZn(BH $_{4}$ ) $_{3}$ , NaZn $_{2}$ (BH $_{4}$ ) $_{5}$ , KZn(BH $_{4}$ ) $_{3}$ , and KZn $_{2}$ (BH $_{4}$ ) $_{5}$ . While LiZn $_{2}$ (BH $_{4}$ ) $_{5}$ , NaZn(BH $_{4}$ ) $_{3}$ , NaZn $_{2}$ (BH $_{4}$ ) $_{5}$ , and KZn(BH $_{4}$ ) $_{3}$ were recently synthesized, LiZn(BH $_{4}$ ) $_{3}$ and KZn $_{2}$ (BH $_{4}$ ) $_{5}$ are hypothetical compounds. Using the minima-hopping method, we discover two new lowest-energy structures for NaZn(BH $_{4}$ ) $_{3}$ and KZn $_{2}$ (BH $_{4}$ ) $_{5}$ which belong to the $C 2 / c$ and $P 2$ space groups, respectively. These structures are predicted to be both thermodynamically stable and dynamically stable, implying that their existence may be possible. On the other hand, we predict that the lowest-energy $P 1$ structure of LiZn(BH $_{4}$ ) $_{3}$ is unstable, suggesting a possible reason elucidating why this compound has not been experimentally identified. In exploring the low-energy structures of these compounds, we find that their energetic ordering is sensitive to the inclusion of the van der Waals interactions. We also find that a proper treatment of these interactions, e.g., as given by a nonlocal density functional such as vdW-DF2, is necessary to address the stability of the low-energy structures of these compounds.

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Received 15 April 2013

DOI:https://doi.org/10.1103/PhysRevB.88.024108

Authors & Affiliations

Tran Doan Huan^1,*, Maximilian Amsler¹, Riccardo Sabatini², Vu Ngoc Tuoc³, Nam Ba Le^3,4, Lilia M. Woods⁴, Nicola Marzari², and Stefan Goedecker^1,†

¹Department of Physics, Universität Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
²Theory and Simulation of Materials, École Polytechnique Fédérale de Lausanne, Station 12, 1015 Lausanne, Switzerland
³Institute of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Road, Hanoi, Vietnam
⁴Department of Physics, University of South Florida, 4202 E. Fowler Ave., Tampa, Florida 33620, USA

^*Current address: Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, USA; Email: huan.tran@ims.uconn.edu
^†stefan.goedecker@unibas.ch

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Issue

Vol. 88, Iss. 2 — 1 July 2013

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