From Small- to Large-Amplitude Dynamics

It is astonishing to see a much similar spectral distribution in the multiplasmon regime (the excitation energy of 10 eV is worth about four plasmons). The dipole resonance thus turns out to be a very robust and harmonic mode. There are, of course, some changes. 

The multiplasmon case leads to broader peaks and an enhanced background, which is due to the larger fluctuations of the mean-field, and to some more electron emission. All spectral hints of the side peaks with little strength are still visible, even more pronounced at the lower-frequency side. 

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