  Here we suggest a simple physical model of HTSC cuprates that provides
qualitative explanation of the main features of these compounds, including the
nature of Fermi arcs, pseudogap anomalies and the origin of free carriers.
According to this model, the unusual properties of HTSC cuprates result from
their unique electronic structure favourable for the formation of diatomic
negative-U centers (NUCs) and realization of an unusual mechanism of
electron-electron interaction.
