Charge density wave (CDW) formation in two-dimensional materials is governed by complex competing lattice instabilities that remain incompletely understood. Here, we investigate the structural evolution of monolayer 1T−VSe2 using first-principles electronic and phonon calculations. The pristine phase exhibits several imaginary-frequency phonon modes associated with dominant instability wave vectors QCDW, which generate the first-generation CDW phases. Subsequent phonon analyses reveal that several of these intermediate structures remain dynamically unstable and undergo further symmetry-lowering distortions into larger superstructures. Through iterative phonon-driven relaxations, we identify multiple transformation pathways that converge toward the same low-energy 23×4 CDW configuration. Although these pathways originate from distinct intermediate CDW states, they ultimately reach nearly degenerate energetically stable phases, demonstrating that different phonon-driven routes can lead to the same ground-state configuration. The results establish a unified phonon-driven cascade mechanism for hierarchical CDW formation in monolayer 1T−VSe2 and provide a systematic framework for understanding competing ordered phases in low-dimensional quantum materials.
@article{arxiv.2605.13458,
title = {Multiple Softening Q-vectors Driving a Cascade of CDW Phases in $\mathrm{1T-VSe}_{2}$},
author = {Zheng-Hong Li and Yung-Ting Lee and Yu-Chan Tai and Cheng-Tien Chiang and Chien-Cheng Kuo and Meng-Kai Lin and Chun-Liang Lin and Hung-Chung Hsueh and Ming-Chiang Chung and Po-Tuan Chen and Chi-Cheng Lee},
journal= {arXiv preprint arXiv:2605.13458},
year = {2026}
}