  The development of novel functional materials in experimental labs combined
with computer-based compound simulation brings the vision of materials design
on a microscopic scale continuously closer to reality. For many applications
interface and surface phenomena rather than bulk properties are key. One of the
most fundamental qualities of a material-vacuum interface is the energy
required to transfer an electron across this boundary, i.e. the work function.
It is a crucial parameter for numerous applications, including organic
electronics, field electron emitters, and thermionic energy converters. Being
generally very resistant to degradation at high temperatures, transition metal
oxides present a promising materials class for such devices. We have performed
a systematic study for perovskite oxides that provides reference values and,
equally important, reports on materials trends and the tunability of work
functions. Our results identify and classify dependencies of the work function
on several parameters including specific surface termination, surface
reconstructions, oxygen vacancies, and heterostructuring.
