A Quantum Chemistry Plus Dynamical Mean Field Approach for Correlated Insulators: Application to La_{2}CuO_{4}

While the traditional local-density approximation (LDA) cannot describe Mott insulators, {\it ab-initio} determination of the Hubbard $U$, for example, limits LDA-plus dynamical mean field theory (DMFT) approaches. Here, we attempt to overcome these bottlenecks by achieving fusion of the quantum chemistry (QC) approach with DMFT. QC+DMFT supplants the LDA bandstructure by its QC counterpart as an input to DMFT. Using QC+DMFT, we show that undoped $La_{2}CuO_{4}$ is a $d$-Mott insulator, and qualitatively discuss the circulating current- and incoherent metal phase, at small but finite hole doping. Very good quantitative agreement with experimental photoemission- and optical spectra constitutes strong support for efficacy of QC+DMFT. Our work thus opens a new avenue for truly {\it ab-initio} correlation-based approaches to describe correlated electronic systems in general.