  The problem of the determination of the nuclear surface and surface symmetry
energy is addressed in the framework of the Extended Thomas Fermi (ETF)
approximation using Skyrme functionals. We propose an analytical model for the
density profiles with variationally determined diffuseness parameters. For the
case of symmetric nuclei, the resulting ETF functional can be exactly
integrated, leading to an analytical formula expressing the surface energy as a
function of the couplings of the energy functional. The importance of non-local
terms is stressed, which cannot be simply deduced from the local part of the
functional. In the case of asymmetric nuclei, we propose an approximate
expression for the diffuseness and the surface energy. These quantities are
analytically related to the parameters of the energy functional. In particular,
the influence of the different equation of state parameters can be explicitly
quantified. Detailed analyses of the different energy components
(local/non-local, isoscalar/isovector, surface/curvature and higher order) are
also performed. Our analytical solution of the ETF integral improves over
previous models and leads to a precision better than 200 keV per nucleon in the
determination of the nuclear binding energy for dripline nuclei.
