▎ 摘　　要

Plasmon excitations in free-standing graphene and graphene/hexagonal boron nitride (hBN) heterostructure are studied using linear-response time-dependent density functional theory within the random phase approximation. Within a single theoretical framework, we examine both the plasmon dispersion behavior and lifetime (linewidth) of Dirac and pi plasmons on an equal footing. Particular attention is paid to the influence of the hBN substrate and the anisotropic effect. Furthermore, a model-based analysis indicates that the correct dispersion behavior of p plasmons should be omega(pi)(q) = root E-g(2) + beta q for small q's, where E-g is the band gap at the M point in the Brillouin zone, and beta is a fitting parameter. This model is radically different from previous proposals, but in good agreement with our calculated results from first principles.