  The relationship between the work function (Phi) and the surface stability of
compounds is, to our knowledge, unknown, but very important for applications
such as organic light-emitting diodes. This relation is studied using
first-principles calculations on various surfaces of BaAl4. The most stable
surface [Ba terminated (001)] has the lowest Phi (1.95 eV), which is lower than
that of any elemental metal including Ba. Adding barium to this surface neither
increases its stability nor lowers its work function. BaAl4 is also strongly
bound. These results run counter to the common perception that stability and a
low Phi are incompatible. Furthermore, a large anisotropy and a stable
low-work-function surface are predicted for intermetallic compounds with polar
surfaces.
