  We present the first ab-initio band-theory-based description of
spin-compensated polarons (known as Zhang-Rice singlets) in a hole-doped
cuprate, specifically one-dimensional Ca_{2+x} Y_{2-x} Cu_5 O_10. Zhang-Rice
singlets are many-particle configurations relevant to the exotic behavior of
hole-doped cuprates, stemming from spontaneous charge localization. They appear
in our case-study material above a threshold doping, successively turning the
insulating undoped antiferromagnet into a gap insulator, a singlet-rich
metallic paramagnet, and finally, a singlet-saturated insulating diamagnet.
