`\ensuremath{\pi}p#39;' mode strongly dispersing in the hexagonal basal plane and almost nondispersing in the perpendicular direction. In the 2.3--3 eV energy range, we find a long-lived intraband plasmon with negative (positive) dispersion with momentum transfer in (perpendicular to) the basal plane. In the 0--1.5 eV energy range, a mode with linear soundlike dispersion along all three high-symmetry directions is observed. All the three modes present strong anisotropy originated from the band structure. The physical origin of these excitation modes is discussed in terms o…" /> `\\ensuremath{\\pi}p

' mode strongly dispersing in the hexagonal basal plane and almost nondispersing in the perpendicular direction. In the 2.3--3 eV energy range, we find a long-lived intraband plasmon with negative (positive) dispersion with momentum transfer in (perpendicular to) the basal plane. In the 0--1.5 eV energy range, a mode with linear soundlike dispersion along all three high-symmetry directions is observed. All the three modes present strong anisotropy originated from the band structure. The physical origin of these excitation modes is discussed in terms of intra- and interband transitions. The crucial role of local field effects in the propagation of the two lowest-energy modes at large momentum transfers and in the determination of its dispersion over extended momentum-transfer region is analyzed.","description":"The low-energy dielectric properties of CaC${}_{6}$---a representative graphite intercalated compound (GIC)---were investigated by $\\mathit{ab}$ $\\mathit{initio}$ time-dependent density functional theory calculations with full inclusion of local field effects. The calculations predict the existence…","datePublished":"2012","isPartOf":{"@type":"Periodical","name":"Physical Review B"},"publisher":{"@type":"Organization","name":"American Physical Society (APS)"},"sameAs":"https://doi.org/10.1103/physrevb.85.205135","identifier":"10.1103/physrevb.85.205135","encoding":{"@type":"MediaObject","contentUrl":"https://libdis.com/api/pdf/1K6hEnsBitWUX1EEQUqq","encodingFormat":"application/pdf"}}