  We present new efficient (O(N log N)) methods for computing three quantities
crucial to electronic structure calculations: the ionic potential, the
electron-ion contribution to the Born-Oppenheimer forces, and the electron-ion
contribution to the stress tensor. The present methods are applicable to
calculations in which the electronic charge density is represented on a uniform
grid in real space. They are particularly well-suited for metallic extended
systems, where other O(N) methodologies are not readily applicable. Based on a
fast algorithm for determining the atomic structure factor, originally
developed by Essmann et al. (U. Essmann, L. Perera, et al.,J. Chem. Phys.
v.103, p.8577 (1995)) for fast Ewald energy and force computation, the present
methods involve approximations that can be systematically improved. The methods
are tested on a representative metallic system (bulk Al),and their ability to
simultaneously achieve high accuracy and efficiency is demonstrated.

Materials Science