  Materials-realistic microscopic theoretical descriptions of copper-based
superconductors are challenging due to their complex crystal structures
combined with strong electron interactions. Here, we demonstrate how density
functional theory can accurately describe key structural, electronic, and
magnetic properties of the normal state of the prototypical cuprate
Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (Bi-2212). We emphasize the importance of
accounting for energy-lowering structural distortions, which then allows us to:
(a) accurately describe the insulating antiferromagnetic (AFM) ground state of
the undoped parent compound (in contrast to the metallic state predicted by
previous {\it ab initio} studies); (b) identify numerous low-energy competing
spin and charge stripe orders in the hole-overdoped material nearly degenerate
in energy with the AFM ordered state, indicating strong spin fluctuations; (c)
predict the lowest-energy hole-doped crystal structure including its long-range
structural distortions and oxygen dopant positions that match high-resolution
scanning microscopy measurements; and (d) describe electronic bands near the
Fermi energy with flat antinodal dispersions and Fermi surfaces that in
agreement with angle-resolved photoemission spectroscopy (ARPES) measurements
and provide a clear explanation for the structural origins of the so-called
``shadow bands''. We also show how one must go beyond band theory and include
fully dynamic spin fluctuations via a many-body approach when aiming to make
quantitative predictions to measure the ARPES spectra in the overdoped
material.
