Fig. 1. Energy absorption spectra of single and double Au atomic chains varying with chain length.(a) Dipole plasmon; (b) Quadrupole plasmon

Fig. 2. Charge distribution at dipole plasmons of five different frequencies. (a) Single atomic chain; (b)-(e) Double atomic chains

Fig. 3. Charge distribution at quadrupole plasmons of three different frequency.(a) Single atomic chain; (b)-(c) Double atomic chains

Fig. 4. Plasmon frequency spectra of single and double Au atomic chains. (a) Dipole plasmon; (b) Quadrupole plasmon