We have computed the surface-plasmon dispersion relation for a metal and compared it with experimental results for Al and Mg. The metal surface is approximated by a step potential and the calculation carried out within the quantum-mechanical random-phase approximation. The integral equation for the self-sustained oscillations is handled by a variational approach. Our dispersion relation is in much better agreement with experimental results than the relation computed for a semi-infinite electron gas.

• Received 31 January 1972

DOI:https://doi.org/10.1103/PhysRevLett.28.1124