Ab initio molecular dynamics: Plane waves vs. local basis: The role of energy cutoff on the convergence of molecular properties

For ab initio molecular dynamics the choice of basis sets (plane waves – PW or localized atomic orbitals – LAO) used is not a trivial issue, since inaccurate results can arise and the extent of these errors are not easily detected. The advantages of each are illustrated for (HF)n clusters. Good agreement with experiment is obtained with LAO while, for the PW approach, electronic energies and IR frequencies are very slowly converging as functions of the cutoff parameter. Basic geometrical parameters oscillate as the cutoff parameter grows, thus it is necessary to properly describe the electronic structure before attempting to include subtler effects.