Ab initio Hellmann-Feynman molecular dynamics for liquid metals

Over the past few years considerable progress has been achieved in ab initio calculations of the structural, electronic, and dynamic properties of liquid and amorphous systems. The fundamental idea was that the equations of motion for the ionic and electronic degrees of freedom may be integrated simultaneously if the electrons are described by a pseudo-Newtonian dynamics. In metallic systems, the original Car-Parrinello approach fails because a transfer of energy from ions to electrons leads to an increase of electronic kinetic energy so that the electrons drift away from the Born-Oppenheimer surface. An alternative is to calculate the Kohn-Sham ground state of the electrons and the exact Hellmann-Feynman forces at each molecular dynamics step. This calculation is now possible using efficient conjugate-gradient techniques for energy minimization and using a subspace alignment for the prediction of the wavefunctions in new ionic configurations.