Excitonic-insulator instability and Peierls distortion in one-dimensional semimetals

The charge density wave instability in one-dimensional semimetals is usually explained through a Peierls-like mechanism, where the coupling of electrons and phonons induces periodic lattice distortion along certain modes vibration, leading to gap opening electronic band structure lowering symmetry lattice. In this work, we study two prototypical Peierls systems: carbon chain monatomic hydrogen with accurate ab initio calculations based on quantum Monte Carlo hybrid functional theory. We demonstrate that at $T=0$, purely can exist independently distortion. It induced by spontaneous formation low energy electron-hole pairs resulting opening, i.e., destabilization semimetallic phase due an excitonic mechanism.