#### Network for Computational Nanotechnology (NCN) Purdue, Norfolk State, Northwestern, MIT, Molecular Foundry, UC Berkeley, Univ.

Download Report#### Transcript Network for Computational Nanotechnology (NCN) Purdue, Norfolk State, Northwestern, MIT, Molecular Foundry, UC Berkeley, Univ.

Network for Computational Nanotechnology (NCN) Purdue, Norfolk State, Northwestern, MIT, Molecular Foundry, UC Berkeley, Univ. of Illinois, UTEP DFT Calculations with Quantum Espresso: User Guide Janam Jhaveri Network for Computational Nanotechnology (NCN) Electrical and Computer Engineering [email protected] 02/07/2011 Janam Jhaveri 2 Janam Jhaveri 3 Quick Initial Run Hit ‘Simulate’ and wait for results Janam Jhaveri 4 Quick Initial Run Under Results you should see: • Density of States plot • Band Structure plot • SCF Output Log • Energy Evolution Plot • Energy, forces and stress data • Input files for quantum espresso executables Janam Jhaveri 5 Janam Jhaveri 6 Janam Jhaveri 7 Input Geometry Atomistic Structure Optional: Select whether to upload input geometry or use a pre-made structure Janam Jhaveri 8 Input Geometry Atomic Coordinates Select whether to use Cartesian or Fractional coordinates Cartesian coordinates: coordinates given in Angstrom using a Cartesian coordinate system (x,y,z) Fractional coordinates: coordinates given in terms of unit cell’s lattice vectors, value must be between 0.0 and 1.0 Janam Jhaveri 9 Input Geometry Structure Type Select structure type See p.11-12 for more info Janam Jhaveri 10 Input Geometry Structure types Simple Cubic (cubic P) Face-Centered Cubic (cubic F) http://en.wikipedia.org/wiki/Crystal_structure Janam Jhaveri 11 Input Geometry Structure types Body-Centered Cubic (cubic I) Hexagonal (Hexagonal and Trigonal P) http://en.wikipedia.org/wiki/Crystal_structure Janam Jhaveri 12 Input Geometry Atomic Coordinates Enter structure (format shown below) Format: Number of atoms Information about structure Atom symbol coordinate 1 coordinate 2 coordinate 3 Atom symbol coordinate 1 coordinate 2 coordinate 3 … Janam Jhaveri 13 Input Geometry Cell Vectors If structure type chosen is ‘Determine unitcell (free)’, enter cell vectors Janam Jhaveri 14 Input Geometry Lattice Parameter a If structure type chosen is NOT ‘Determine unitcell (free)’, enter lattice parameter a See p. 11-13 for definition of lattice parameter a Janam Jhaveri 15 Input Geometry Lattice Parameter c If structure type chosen is ‘Hexagonal and Trigonal P’, also enter the ratio between lattice parameters c and a See p. 12 for definition of lattice parameter c Janam Jhaveri 16 Janam Jhaveri 17 Energy Expression Functional Select either LDA or GGA (PBE) for ExchangeCorrelation functional See p. 19 for more info Janam Jhaveri 18 Energy Expression Exchange-correlation energies LDA (Local Density Approximation): approximations of exchange-correlation energies that depend only on value of electronic density at each point in space GGA (Generalized Gradient Approximation): still local, but also includes gradient of density at that point in space Quantum Espresso uses pseudopotentials to implement exchange-correlation energies. Pseudopotentials are approximations of the wavefunctions of valence electrons in the nuclear core region. This leads to a modified potential term instead of Coulombic potential term in the Schrodinger Equation. Pseudopotentials for atoms are available as specified by http://www.pwscf.org/pseudo.php Janam Jhaveri 19 Energy Expression Relax Optional: Select either force or cell relaxation Force Relax: minimize forces while keeping the unit cell boundaries fixed Cell Relax: allow the unit cell boundaries to relax Janam Jhaveri 20 Energy Expression K-grid Select number of k-points to be used in the x, y and zdirection Janam Jhaveri 21 Energy Expression Bands Select number of bands Janam Jhaveri 22 Energy Expression Energy cutoffs Select energy cutoffs and selfconsistent field (SCF) convergence criterion Janam Jhaveri 23 Energy Expression Occupation Options Optional: Enable occupation options and select occupation See p. 27 for more info on occupation options Janam Jhaveri 24 Energy Expression Smearing If Occupation selected is ‘smearing’, choose a smearing type See p. 28 for more info on smearing options Janam Jhaveri 25 Energy Expression Gaussian Spreading If Occupation selected is ‘smearing’, enter a value for the Gaussian spreading/broadening Janam Jhaveri 26 Energy Expression Occupation Options source: http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3900903 “smearing: Gaussian smearing for metals tetrahedra: for calculation of DOS in metals (see PRB49, 16223 (1994)) Not suitable (because not variational) for force/optimization/dynamics calculations fixed: for insulators with a gap“ Janam Jhaveri 27 Energy Expression Smearing Options source: http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3900938 “Gaussian: ordinary Gaussian spreading Methfessel-Paxton: Methfessel-Paxton first-order spreading (see PRB 40, 3616 (1989)) Marzari-Vanderbilt: Marzari-Vanderbilt cold smearing (see PRL 82, 3296 (1999)) Fermi-Dirac: smearing with Fermi-Dirac function” Janam Jhaveri 28 Energy Expression Mixing Options Optional: Enable mixing options and select mixing mode See p. 31 for more info on mixing modes Janam Jhaveri 29 Energy Expression Mixing factor Enter a value for the mixing factor Janam Jhaveri 30 Energy Expression Mixing modes source: http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3901509 “plain: charge density Broyden TF : as above, with simple Thomas-Fermi screening (for highly homogeneous systems) local-TF: as above, with local-density-dependent TF screening (for highly inhomogeneous systems)” Janam Jhaveri 31 Janam Jhaveri 32 Phonons Phonon Calculations Optional: select whether to perform phonon calculations Janam Jhaveri 33 Phonons Calculation type Select whether to perform dispersion relationship or a single q-point calculation Janam Jhaveri 34 Phonons Atomic Mass Enter list of atom types and their mass in amu (format shown below) Format: Atom symbol mass Atom symbol mass … Janam Jhaveri 35 Phonons Convergence criterion Enter energy value as phonon convergence criterion. Note energy is given in Ry. Janam Jhaveri 36 Phonons Dielectric constant Optional: choose to calculate macroscopic dielectric constant Warning: will not work with metallic systems Janam Jhaveri 37 Phonons Q-grid spacing If you’re doing a dispersion relationship calculation, select number of q-points to be used in the x, y and z- direction Janam Jhaveri 38 Phonons Dispersion curve path If you’re doing a dispersion relationship calculation, select high symmetry points (Qpoints) for the path. Q-points should be given in fractional (reduced) coordinates. Janam Jhaveri 39 Phonons Number of points Enter number of points on dispersion curve path Janam Jhaveri 40 Phonons Single q-point If you’re doing a single Qpoint calculation, choose Qpoint on which to do phonon calculations Janam Jhaveri 41 Janam Jhaveri 42 Band structure Band structure Calculations Optional: select whether to perform band structure calculations Janam Jhaveri 43 Band structure Band structure path Select high symmetry points (K-points) along which the path should be plotted. K-points should be given in fractional (reduced) coordinates. Janam Jhaveri 44 Band structure Number of points on path Enter number of points on band structure path Janam Jhaveri 45 Density of States Minimum Energy Enter minimum of energy grid to plot. Note energy is given in eV. Janam Jhaveri 46 Density of States Maximum Energy Enter maximum of energy grid to plot Janam Jhaveri 47 Density of States Energy grid step Enter energy grid step to plot Janam Jhaveri 48 References • http://en.wikipedia.org/wiki/Crystal_structure • http://www.pwscf.org/pseudo.php • http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3900903 • http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3900938 • http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3901509 Janam Jhaveri 49