title: Electron-phonon coupling and the metallization of solid helium at terapascal pressures.
abstract: Solid He is studied in the pressure and temperature ranges 1-40 TPa and 0-10 000 K using first-principles methods. Anharmonic vibrational properties are calculated within a self-consistent field framework, including the internal and free energies, density-pressure relation, stress tensor, thermal expansion, and the electron-phonon coupling renormalization of the electronic band gap. We find that an accurate description of electron-phonon coupling requires us to use a nonperturbative approach. The metallization pressure of 32.9 TPa at 0 K is larger than found previously. The vibrational effects are large; for example, at P=30  TPa the band gap is increased by 2.8 eV by electron-phonon coupling and a further 0.1 eV by thermal expansion compared to the static value. The implications of the calculated metallization pressure for the cooling of white dwarfs are discussed.
authors.affiliation: TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Bartomeu
authors.initials: B
authors.lastname: Monserrat
authors.affiliation: Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom.
authors.forename: N D
authors.initials: ND
authors.lastname: Drummond
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Pickard
authors.affiliation: TCM Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: R J
authors.initials: RJ
authors.lastname: Needs