We have used the Car-Parrinello AIMD scheme, where the electron density and total energy were calculated in the local density approximation (LDA) with Vosco's parameterized form for the exchange-correlation energy.
The valence electronic wave functions were expanded in plane waves, and their interactions with nuclei and the core electrons were described through the generalized norm-conserving Hamman's pseudopotentials. The nonlocal part of pseudopotentials was modified to a completely separable form as suggested by Kleinman and Bylander. Since the original Hamman's pseudopotential requires too high cut-off energy for oxygen, a softer potential was constructed by increasing the core radii.
We used the cut-off energyof 100 Ry which required about 130 000 plane waves for each molecular orbital in the cubic cell with a size of 20 a.u. We replaced hydrogens by deuterium atoms in order to be able to use large values for the time step (D = 7 a.u.) and fictitious mass (m = 1100 a.u.) in Carr-Parrinello dynamics.
Because we are dealing with charged isolated clusters with the strong dipoles and long-range Coulomb interactions, a Hockney aperiodic convolution method for solving Poisson's equations for non-periodic systems with free-space boundary conditions has been used.
Ab initio molecular dynamics of aluminum solvation
by Mark I. Lubin and John H. Weare, UCSD