  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 LDA+U approximation. We observe that the inclusion of electron
correlation in a mean-field level as implemented in the 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.
