title: Non-self-consistent Density-Functional Theory Exchange-Correlation Forces for GGA Functionals.
abstract: When using density functional theory (DFT), generalized gradient approximation (GGA) functionals are often necessary for accurate modeling of important properties of biomolecules, including hydrogen-bond strengths and relative energies of conformers. We consider the calculations of forces using non-self-consistent (NSC) methods based on the Harris-Foulkes expression for energy. We derive an expression for the GGA NSC force on atoms, valid for a hierarchy of methods based on local orbitals, and discuss its implementation in the linear scaling DFT code Conquest, using a standard (White-Bird) approach. We investigate the use of NSC structural relaxations before full self-consistent relaxations as a method for improving convergence. Example calculations for glycine and small alanine peptides suggest that NSC pre-relaxations of the structure are indeed useful to save computer effort and time.
authors.affiliation: London Centre for Nanotechnology, UCL, 17-19 Gordon St, London WC1H 0AH, U.K., and Materials Simulation Laboratory and Department of Physics and Astronomy, UCL, Gower St, London WC1E 6BT, and National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0045, JAPAN.
authors.forename: Antonio S
authors.initials: AS
authors.lastname: Torralba
authors.affiliation: London Centre for Nanotechnology, UCL, 17-19 Gordon St, London WC1H 0AH, U.K., and Materials Simulation Laboratory and Department of Physics and Astronomy, UCL, Gower St, London WC1E 6BT, and National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0045, JAPAN.
authors.forename: David R
authors.initials: DR
authors.lastname: Bowler
authors.affiliation: London Centre for Nanotechnology, UCL, 17-19 Gordon St, London WC1H 0AH, U.K., and Materials Simulation Laboratory and Department of Physics and Astronomy, UCL, Gower St, London WC1E 6BT, and National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0045, JAPAN.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Miyazaki
authors.affiliation: London Centre for Nanotechnology, UCL, 17-19 Gordon St, London WC1H 0AH, U.K., and Materials Simulation Laboratory and Department of Physics and Astronomy, UCL, Gower St, London WC1E 6BT, and National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0045, JAPAN.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gillan