  We present results for the momentum-resolved single-particle spectral
function of the low-dimensional system TiOCl in the insulating state, obtained
by a combination of ab initio Density Functional Theory (DFT) and Variational
Cluster (VCA) calculations. This approach allows to combine a realistic band
structure and a thorough treatment of the strong correlations. We show that it
is important to include a realistic two-dimensional band structure of TiOCl
into the effective strongly-correlated models in order to explain the spectral
weight behavior seen in angle-resolved photoemission (ARPES) experiments. In
particular, we observe that the effect of the interchain couplings is a
considerable redistribution of the spectral weight around the Gamma point from
higher to lower binding energies as compared to a purely one-dimensional model
treatment. Hence, our results support a description of TiOCl as a
two-dimensional compound with strong anisotropy and also set a benchmark on the
spectral features of correlated coupled-chain systems.
