We present first-principles frozen-phonon calculations for the three Raman-active $A_g$ modes in the spin-$1∕2$-layered TiOCl system within two different well-known approaches: the local-density approximation (LDA) and the so-called $\mathrm{LDA}+U$ approximation. We observe that the inclusion of electron correlation in a mean-field level as implemented in the $\mathrm{LDA}+U$ leads to a better overall agreement with experimental results. We also discuss the implications of the two approaches on the physics of TiOCl.

• Received 4 February 2005

DOI:https://doi.org/10.1103/PhysRevB.71.180409