Nonlinear electron dynamics in metal clusters

Recent experimental developments give more and more access to cluster excitations beyond the regime of linear response. Most theoretical descriptions of the induced nonlinear electron dynamics are based on the time-dependent local density approximation (TDLDA) and related schemes. We review the present status of TDLDA calculations for metal clusters, considering formal aspects of the theory, recipes for its numerical implementation as well as a variety of applications. These applications are presented by first summarizing basic linear spectral properties of the systems under study and then introducing two mechanisms for strong excitations: collision with highly charged and fast ions, and irradiation with strong femtosecond laser pulses. We present results for observables that are relevant for experiments, including ionization, energy balance, second-harmonic generation, electron emission spectra and, last but not least, we discuss the effects of ionic motion during the electronic dynamics. On the theoretical side, we also discuss semiclassical approaches and extensions beyond TDLDA, such as self-interaction corrections and the influence of electron–electron collisions.