  The quantitative description of correlated electron materials remains a
modern computational challenge. We demonstrate a numerical strategy to simulate
correlated materials at the fully ab initio level beyond the solution of
effective low-energy models, and apply it to gain a detailed microscopic
understanding across a family of cuprate superconducting materials in their
parent undoped states. We uncover microscopic trends in the electron
correlations and reveal the link between the material composition and magnetic
energy scales via a many-body picture of excitation processes involving the
buffer layers. Our work illustrates a path towards a quantitative and reliable
understanding of more complex states of correlated materials at the ab initio
many-body level.
