Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, PL31-342 Kraków, Poland.
Phys Chem Chem Phys. 2018 Dec 12;20(48):30140-30149. doi: 10.1039/c8cp02371a.
Solid state closo-borane salts of alkali metals have very high ionic conductivity. This makes them interesting for practical applications as solid state electrolytes, and has triggered extensive research efforts. Improvement and understanding of their properties require accurate theoretical description of their static and dynamical properties. In this work, we report accuracy assessment of density functional theory in the description of solids with B12H122- anions. We show that these aromatic anions interact via weak dispersive forces. For that reason, non-local exchange-correlation functionals give better description of structural properties and phonons in Li2B12H12 and Na2B12H12. Numerically efficient semi-local methods provide satisfactory results when applied in structure volumes obtained in a non-local method. An extensive structural search for stable crystalline phases of MgB12H12 predicts a new denser lattice with C2/c symmetry that is stabilized by van der Waals interactions. These structures might be discovered as anhydrous MgB12H12 in high pressure experiments, avoiding the amorphous state at ambient pressures.
碱金属的固态笼状硼烷盐具有非常高的离子电导率。这使得它们作为固态电解质在实际应用中很有趣，并引发了广泛的研究。为了改善和理解它们的性质，需要准确地描述它们的静态和动态特性。在这项工作中，我们报告了密度泛函理论在描述 B12H122-阴离子固体中的准确性评估。我们表明，这些芳香阴离子通过弱色散力相互作用。因此，非局部交换相关泛函能更好地描述 Li2B12H12 和 Na2B12H12 的结构性质和声子。在非局部方法获得的结构体积中应用数值效率高的半局部方法可以得到令人满意的结果。对 MgB12H12 稳定晶相的广泛结构搜索预测了一种具有 C2/c 对称性的新的更密集的晶格，该晶格通过范德华相互作用稳定。这些结构可能在高压实验中以无水 MgB12H12 的形式被发现，从而避免了常压下的非晶态。
