  An ab initio pseudopotential method based on density functional theory,
generalized gradient corrections to exchange and correlation, and
projector-augmented waves is used to investigate structural, energetical,
electronic and optical properties of MgO, ZnO, and CdO in rocksalt, cesium
chloride, zinc blende, and wurtzite structure. In the case of MgO we also
examine the nickel arsenide structure and a graphitic phase. The stability of
the ground-state phases rocksalt (MgO, CdO) and wurtzite (ZnO) against
hydrostatic pressure and biaxial strain is studied. We also present the band
structures of all polymorphs as well as the accompanying dielectric functions.
We discuss the physical reasons for the anomalous chemical trend of the
ground-state geometry and the fundamental gap with the size of the group-II
cation in the oxide. The role of the shallow Zn3d and Cd4d electrons is
critically examined.
