Hole Doping and Inhomogeneous Charge Distribution in High Tc Cuprates Investigated from First Principles

To understand the link between doping and electronic properties in the high-temperature superconductors, we have performed first-principles calculations for several representatives of high T_c compounds. In the single-layer cuprate HgBa₂CuO₄ the excess oxygen attracts electrons from the CuO₂ plane leading to an increase of the hole concentration in this building block, where the maximum amount of holes is reached when the dopant oxygen shell is closed. The usage of supercells allows to study the inhomogeneous charge distribution as a function of doping, i.e. from the underdoped up to the overdoped regime. Comparison is made with other compounds like Ba-doped La₂CuO₄ and oxygen-deficient YBa₂Cu₃O_7–x. The effects of our findings on superconductivity are discussed.