Determination of the electron effective band mass in amorphous carbon from density-functional theory calculations

We generate a series of amorphous carbon materials of densities varying between 2.0 and 3.5 g/cm(3). Their dielectric functions are calculated within the density-functional theory approach, and the low-loss electron energy-loss spectra are evaluated. The dependence of the pi+sigma plasmon energy E-p on the valence electron density (n(e)) is determined. We find that the free-electron model in which E(p)proportional ton(e)(0.5) is valid. The coefficient of proportionality leads to a ratio of the electron-effective band mass m(*) to the free-electron mass m of m(*)/m=0.87, which is the value obtained using measurements based on the grazing-angle x-ray reflectivity and electron energy-loss spectroscopy [see A. C. Ferrari, Phys. Rev. B 62, 11089 (2000) ]. This result supports the reliability of amorphous carbon mass densities obtained from EELS data when an electron-effective mass of 0.87 m is used.