Laser-induced breathing modes in metallic nanoparticles: a symmetric molecular dynamics study.

A highly efficient simulation method based on molecular dynamics and group theory is adopted to investigate the laser-induced breathing oscillation of gold and silver nanospheres. Nanoparticles with size ranging from 5.8 to 46.2 nm are discussed. The effect due to laser-induced heating is modeled by a symmetric sudden expansion of the nanospheres by increasing the interatomic distances. A long-range empirical potential model which is capable of describing the phonon dispersion curves of noble metals in the full frequency range is established. Group theory is fully exploited to increase the computation efficiency, and the oscillation behavior of nanospheres of over 3 × 10(6) atoms can be simulated efficiently. Oscillation frequencies of nanospheres are obtained by calculating the Fourier transform of the velocity autocorrelation function. The breathing modes of nanospheres are identified as the excitation of A(1g) modes with in-phase radial displacement of atoms in the nanospheres. The resulting oscillation spectra are in very good agreement with experimental data.