Neutron drops and Skyrme energy-density functionals.

The {ital J}{sup {pi}}=0{sup +} ground state of a drop of 8 neutrons and the lowest 1/2{sup {minus}} and 3/2{sup {minus}} states of 7-neutron drops, all in an external well, are computed accurately with variational and Green{close_quote}s function Monte Carlo methods for a Hamiltonian containing the Argonne {ital v}{sub 18} two-nucleon and Urbana IX three-nucleon potentials. These states are also calculated using Skyrme-type energy-density functionals. Commonly used functionals overestimate the central density of these drops and the spin-orbit splitting of 7-neutron drops. Improvements in the functionals are suggested. {copyright} {ital 1996 The American Physical Society.}