Crystal structure prediction of lithium-beryllium alloys under pressure with distinctive electronic and dynamic behaviors

Using machine learning--assisted crystal structure search and first-principles calculations, we have unveiled two hitherto undiscovered thermodynamically stable stoichiometries, namely, Cmmm $\mathrm{Li}{\mathrm{Be}}_{5}$ and $R\overline{3}m\phantom{\rule{4pt}{0ex}}\mathrm{Li}{\mathrm{Be}}_{6}$, alongside a metastable phase, Cmca LiBe, within the high-pressure realm of Li-Be alloys. Moreover, our investigation has illuminated the distinctive electronic characteristics of Cmca LiBe and $R\overline{3}$$m\phantom{\rule{4pt}{0ex}}\mathrm{Li}{\mathrm{Be}}_{6}$, both capable of accommodating quasi-two-dimensional electrons, a feature conspicuously absent in $\mathrm{Li}{\mathrm{Be}}_{5}$. Additional molecular dynamic simulations also prove the existence of a superionic state in previously discovered $P{2}_{1}/m$ LiBe and $C2$/$m\phantom{\rule{4pt}{0ex}}\mathrm{L}{\mathrm{i}}_{3}\mathrm{Be}$. More interestingly, the Li atoms in $P{2}_{1}/m$ LiBe only diffuse in one direction due to the potential well and interstitial electrons. Our study not only enriches the phase diagram of Li-Be alloys but also provides a solid theoretical foundation for future experimental investigations.