Born–Oppenheimer dynamics using density-functional theory: Equilibrium and fragmentation of small sodium clusters

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Abstract
The properties of small neutral and positively charged sodium clusters and the fragmentation dynamics of Na++4 are investigated using a simulation technique which combines classical molecular dynamics on the electronic Born–Oppenheimer ground‐state potential surface with electronic structure calculations via the local spin‐density functional method. Results for the optimal energies and structures of Nan and Na+n (n≤4) are in quantitative agreement with previous studies and experimental data. Fission of Na++4 on its ground state Born–Oppenheimer potential‐energy surface, following sudden ionization of selected configurations of an Na+4 (or Na4) cluster, whose vibrational energy content corresponds to 300 K, is found to occur on a picosecond time scale. The preferred fission channel is found to be Na+3+Na+, with an interfragment relative translational kinetic energy of ∼2 eV, and a vibrationally excited Na+3. The dynamics of the fragmentation process is analyzed.