We show that an ab initio molecular-dynamics scheme based on Vanderbilt ultrasoft pseudopotentials and a plane-wave expansion for the electronic orbitals allows one to perform accurate calculations for large systems containing tightly bound d-electron states. We use a novel real-space double-grid technique to deal efficiently with the localized augmentation functions in the core region. We apply our scheme in a full molecular-dynamics simulation of liquid copper at a temperature of 1500 K and find structural and dynamical properties that are in excellent agreement with experimental data.