  Quantum computers (QC) could harbor the potential to significantly advance
materials simulations, particularly at the atomistic scale involving strongly
correlated fermionic systems where an accurate description of quantum many-body
effects scales unfavorably with size. While a full-scale treatment of condensed
matter systems with currently available noisy quantum computers remains
elusive, quantum embedding schemes like dynamical mean-field theory (DMFT)
allow the mapping of an effective, reduced subspace Hamiltonian to available
devices to improve the accuracy of ab initio calculations such as density
functional theory (DFT). Here, we report on the development of a hybrid
quantum-classical DFT+DMFT simulation framework which relies on a quantum
impurity solver based on the Lehmann representation of the impurity Green's
function. Hardware experiments with up to 14 qubits on the IBM Quantum system
are conducted, using advanced error mitigation methods and a novel calibration
scheme for an improved zero-noise extrapolation to effectively reduce adverse
effects from inherent noise on current quantum devices. We showcase the utility
of our quantum DFT+DMFT workflow by assessing the correlation effects on the
electronic structure of a real material, Ca2CuO2Cl2, and by carefully
benchmarking our quantum results with respect to exact reference solutions and
experimental spectroscopy measurements.
