MOLECULAR-DYNAMICS WITH QUANTUM FORCES - VIBRATIONAL-SPECTRA OF LOCALIZED SYSTEMS

We present molecular-dynamics simulations with quantum forces for loca lized systems using a real-space method. We illustrate calculations fo r the vibrational modes of small molecules and clusters. Unlike other real-space methods using adaptive grids, this procedure does not requi re any Pulay corrections for the forces, nor does it suffer from the c omplication of redefining a grid after each time step of the molecular -dynamics simulation. Our method is based on combining higher order fi nite difference methods with ab initio pseudopotentials. We also intro duce an iterative diagonalization scheme based on preconditioned Krylo v techniques. Compared to plane-wave-supercell methods, this method is more efficient and simpler to implement. Examples are presented for t he CO2 molecule and a silicon cluster, Si-4.