  We analyze the ground state energy and spin of quantum dots obtained from
spin density functional theory (SDFT) calculations. First, we introduce a
Strutinsky-type approximation, in which quantum interference is treated as a
correction to a smooth Thomas-Fermi description. For large irregular dots, we
find that the second-order Strutinsky expressions have an accuracy of about 5
percent compared to the full SDFT and capture all the qualitative features.
Second, we perform a random matrix theory/random plane wave analysis of the
Strutinsky SDFT expressions. The results are statistically similar to the SDFT
quantum dot statistics. Finally, we note that the second-order Strutinsky
approximation provides, in essence, a Landau Fermi liquid picture of spin
density functional theory. For instance, the leading term in the spin channel
is simply the familiar exchange constant. A direct comparison between SDFT and
the perturbation theory derived ``universal Hamiltonian'' is thus made
possible.
