We present a first-principles study based on density functional theory (DFT) on the electronic and structural properties of Ta2NiSe5, a layered transition metal chalcogenide that has been considered as a possible candidate for an excitonic insulator. Our systematic DFT results however provide a non-excitonic mechanism for the experimentally observed electronic and structural phase transitions in Ta2NiSe5, in particular explaining why sulfur substitution of selenium reduces the distortion angle in the low-temperature phase and potassium dosing closes the gap in the electronic structure. Moreover, the calculations show that these two effects couple to each other. Further, our first-principles calculations predict several changes in both the crystal structure and electronic structure under the effects of uniform charge dosing and uniaxial strain, which could be tested experimentally.
@article{arxiv.2505.17324,
title = {Non-excitonic mechanism for electronic and structural phase transitions in Ta2Ni(Se,S)5},
author = {Weichen Tang and Zhenglu Li and Cheng Chen and Yu He and Steven G. Louie},
journal= {arXiv preprint arXiv:2505.17324},
year = {2025}
}