Maximally charged single-pair multi-Weyl point phonons in P23 -type BeH2

The realization of multi-Weyl systems with the minimum nonzero number of Weyl points and the maximum charge number remains challenging in topology physics. In this work, based on first-principles calculations, we propose that ${\mathrm{BeH}}_{2}$ is thermodynamically, mechanically, and dynamically stable in a cubic crystal structure with the $P23$ space group. Importantly, this is the first work to report the appearance of single-pair multi-Weyl point phonons with the maximum charge number in $P23$-type ${\mathrm{BeH}}_{2}$. Furthermore, the number and charge of the Weyl points and the phononic surface modes can be tuned by applying $1%$ and $2%$ uniaxial strains along the [100] and [111] directions, respectively. Finally, we report that clean charge-two single-pair triple-point phonons appear in $P23$-type ${\mathrm{BeH}}_{2}$ and investigate the related chiral phonon transition under the uniaxial strains.