Anharmonic effect driven topological phase transition inPbO2predicted by first-principles calculations

The crystal structures and electronic structures of lead dioxide are investigated with ab initio calculations. We find the previously known tetragonal $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$ (space group: $P{4}_{2}/mnm$) is dynamically unstable at low temperature due to the existence of a vibrational soft mode under the harmonic approximation, and it becomes stable at finite temperature about 200 K attributed to the enhanced anharmonic effect. Under the guidance of the vibrational soft mode, we find an orthorhombic structure (space group: Pnnm) that is a candidate of the ground state of $\mathrm{Pb}{\mathrm{O}}_{2}$ at low temperature. Electronic structure calculations suggest the low-temperature orthorhombic phase is a trivial insulator, while the tetragonal high-temperature phase is a topological Dirac nodal line semimetal. Therefore, there is a topological phase transition from a trivial insulator to a topological semimetal in $\mathrm{Pb}{\mathrm{O}}_{2}$, strongly coupled with the stabilized soft mode and thus anharmonicity-driven structural transformation. For future experiment verification, the results for the temperature dependence of x-ray diffraction and Raman spectra are also provided. Our work demonstrates the important role of anharmonicity in describing the structural phase transition and exploits the impact of anharmonicity to the topological property of the system.