  The structural and electronic properties of the LaAlO3/Si(001) interface are
determined using state-of-the-art electronic structure calculations. The atomic
structure differs from previous proposals, but is reminiscent of La adsorption
structures on silicon. A phase diagram of the interface stability is calculated
as a function of oxygen and Al chemical potentials. We find that an
electronically saturated interface is obtained only if dopant atoms segregate
to the interface. These findings raise serious doubts whether LaAlO3 can be
used as an epitaxial gate dielectric.
