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In computer-experimental studies of surface vibrations in monatomic crystals, surface modes of a new type have been found near the Brillouin zone boundary in gaps between bands of different kinds of bulk modes (e.g., longitudinal and transverse). Other surface modes, including Rayleigh waves and extra high- or low-frequency modes when adsorbed films are present, have also been found and investigated.
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Allen et al. (1969) studied this question.
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