Intercalant and intermolecular phonon assisted superconductivity in K-doped picene

K3 picene is a superconducting molecular crystal with a critical temperature of Tc=7 or 18 K, depending on the preparation conditions. Using density functional theory we show that electron-phonon interaction accounts for Tc 3-8 K. The average electron-phonon coupling, calculated by including the phonon energy scale in the electron-phonon scattering, is λ=0.73 and ωlog=18.0meV. Intercalant and intermolecular phonon modes contribute substantially (40%) to λ as also shown by the isotope exponents of potassium (0.19) and carbon (0.31). The relevance of these modes makes superconductivity in K-doped picene peculiar and different from that of fullerenes. © 2011 American Physical Society.