A plane-wave pseudopotential description of charged clusters

One of the most efficient approaches in computational cluster physics uses a plane-wave basis set and pseudopotentials to describe electron-ion intera ctions. This method - where the dusters are placed inside supercells - is r estricted in its usual form to neutral systems because of the long-range in teraction between a charged cluster and its periodic images. To eliminate t his restriction, Ne propose to shield each charged cluster with a spherical shell having a symmetric charge that neutralizes the supercell. Furthermor e, the shell is placed in such a way that it cancels the electric dipole of the charged cluster. We present relaxed geometries and cohesive energies o f Na-N(+), N= 2-9 and 21, obtained with Langevin quantum molecular dynamics . Our local density approximation structures are very similar to those foun d in other first principles calculations. Vertical and adiabatic ionization energies of Na-N, N = 2, 3, 6, and 8 are displayed. We also show results f or Na-8(2+), Na-5(-) and Na-7(-).