[en] HfO₂ is a prominent candidate for applications necessitating the use of high-k dielectrics. It could e.g. replace SiO₂ layers in small-sized (DE) metal-oxide semiconductor devices (MOS). Thus the electrical and structural properties of HfO₂ have to be investigated. Using first principles methods, the properties of charged oxygen vacancies in cubic HfO₂ have been analysed, because they are probably one of the major traps contributing to charge trapping in HfO₂. Although the cubic phase is the high temperature phase, it is frequently found in HfO₂ thin films. With the help of supercell calculations the formation energy of differently charged oxygen vacancies in this phase are determined. This will help to understand the nature of defects in this material and consequently to understand the electrical properties. Differently charged states (-2, -1, 0, +1 and +2) of the defect systems have been relaxed with an optimisation algorithm and a bandstructure calculation of HfO₂ bulk has been performed. With these calculations we intend to study the nature of the defect levels in the band gap, e.g. whether they show negative-U behaviour. This can help to understand the electronic transport mechanism in HfO₂