On the basis of ab initio density functional theory (DFT) calculations, we derive the underlying microscopic model Hamiltonian for TiOCl, a unique system that shows two consecutive phase transitions from a Mott insulator to a spin-Peierls insulator through a structurally incommensurate phase. We show with our model that the presence of magnetic frustration in TiOCl leads to a competition with the spin-Peierls distortion, which results in the novel incommensurate phase. In addition, our calculations indicate that the spin-Peierls state is triggered by adiabatic phonons, which is essential for understanding the nature of the phase transition.
@article{arxiv.0804.3342,
title = {Microscopic model for transitions from Mott to spin-Peierls insulator in TiOCl},
author = {Yu-Zhong Zhang and Harald O. Jeschke and Roser Valenti},
journal= {arXiv preprint arXiv:0804.3342},
year = {2008}
}