  The s manifold energy levels for phosphorus donors in silicon are important
input parameters for the design and modelling of electronic devices on the
nanoscale. In this paper we calculate these energy levels from first principles
using density functional theory. The wavefunction of the donor electron's
ground state is found to have a form that is similar to an atomic s orbital,
with an effective Bohr radius of 1.8 nm. The corresponding binding energy of
this state is found to be 41 meV, which is in good agreement with the currently
accepted value of 45.59 meV. We also calculate the energies of the excited
1s(T) and 1s(E) states, finding them to be 32 and 31 meV respectively. These
results constitute the first ab initio confirmation of the s manifold energy
levels for phosphorus donors in silicon.
