FIRST PRINCIPLES CALCULATION OF THE THERMODYNAMIC PROPERTIES OF SILICON CLUSTERS

The thermodynamic properties of Si clusters are calculated using first principles quantum methods combined with molecular dynamics for simul ating the trajectories of clusters. A plane wave basis is used with ab initio pseudo potentials and the local density approximation for dete rmining the electronic energies and forces. Langevin molecular dynamic s simulates thermal contact with a constant temperature reservoir. Vib rational spectra, moments of inertia, anharmonic corrections, and free energies are predicted for Si-2 through Si-5. The translational contr ibution is based on the ideal gas limit. The rotation contribution is approximated using a classical rigid rotator. Vibrational modes are de termined from the dynamical matrix in the harmonic approximation. Corr ections due to anharmonicity and coupling between rotational and vibra tional modes are fit from the molecular dynamics simulations.