  We present an ab initio GW calculation to study dynamical effects on an
organic compound (TMTSF)2PF6. Calculated polarized reflectivities reproduce
experimental plasma edges at around 0.2 eV for E||b' and 1.0 eV for E||a. The
low-energy plasmons come out from the low-energy narrow bands energetically
isolated from other higher-energy bands, and affect the low-energy electronic
structure via the GW-type self-energy. Because of the quasi-one-dimensional
band structure, a large plasmon-induced electron scattering is found in the
low-energy occupied states along the X-M line.
