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 02/07/2011

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Quick Initial Run Hit ‘Simulate’ and wait for results 4

Janam Jhaveri Quick Initial Run 5 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 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

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Input Geometry Atomistic Structure 8 Optional: Select whether to upload input geometry or use a pre-made structure

Janam Jhaveri Input Geometry Atomic Coordinates 9 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 Input Geometry Structure Type 10 Select structure type See p for more info Select structure type See p for more info

Janam Jhaveri Input Geometry Structure types 11 Simple Cubic (cubic P)Face-Centered Cubic (cubic F)

Janam Jhaveri Input Geometry Structure types 12 Body-Centered Cubic (cubic I)Hexagonal (Hexagonal and Trigonal P)

Janam Jhaveri Input Geometry Atomic Coordinates 13 Enter structure (format shown below) Format: Number of atoms Information about structure Atom symbol coordinate 1 coordinate 2 coordinate 3 … Format: Number of atoms Information about structure Atom symbol coordinate 1 coordinate 2 coordinate 3 …

Janam Jhaveri Input Geometry Cell Vectors 14 If structure type chosen is ‘Determine unitcell (free)’, enter cell vectors

Janam Jhaveri Input Geometry Lattice Parameter a 15 If structure type chosen is NOT ‘Determine unitcell (free)’, enter lattice parameter a See p for definition of lattice parameter a If structure type chosen is NOT ‘Determine unitcell (free)’, enter lattice parameter a See p for definition of lattice parameter a

Janam Jhaveri Input Geometry Lattice Parameter c 16 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 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

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Janam Jhaveri Energy Expression Functional 18 Select either LDA or GGA (PBE) for Exchange- Correlation functional See p. 19 for more info Select either LDA or GGA (PBE) for Exchange- Correlation functional See p. 19 for more info

Janam Jhaveri Energy Expression Exchange-correlation energies 19 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

Janam Jhaveri Energy Expression Relax 20 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 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 Energy Expression K-grid 21 Select number of k-points to be used in the x, y and z- direction

Janam Jhaveri Energy Expression Bands 22 Select number of bands

Janam Jhaveri Energy Expression Energy cutoffs 23 Select energy cutoffs and self- consistent field (SCF) convergence criterion

Janam Jhaveri Energy Expression Occupation Options 24 Optional: Enable occupation options and select occupation See p. 27 for more info on occupation options Optional: Enable occupation options and select occupation See p. 27 for more info on occupation options

Janam Jhaveri Energy Expression Smearing 25 If Occupation selected is ‘smearing’, choose a smearing type See p. 28 for more info on smearing options If Occupation selected is ‘smearing’, choose a smearing type See p. 28 for more info on smearing options

Janam Jhaveri Energy Expression Gaussian Spreading 26 If Occupation selected is ‘smearing’, enter a value for the Gaussian spreading/broadening

Janam Jhaveri Energy Expression Occupation Options source: 27 “smearing: Gaussian smearing for metals tetrahedra: for calculation of DOS in metals (see PRB49, (1994)) Not suitable (because not variational) for force/optimization/dynamics calculations fixed: for insulators with a gap“

Janam Jhaveri Energy Expression Smearing Options source: 28 “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 Energy Expression Mixing Options 29 Optional: Enable mixing options and select mixing mode See p. 31 for more info on mixing modes Optional: Enable mixing options and select mixing mode See p. 31 for more info on mixing modes

Janam Jhaveri Energy Expression Mixing factor 30 Enter a value for the mixing factor

Janam Jhaveri Energy Expression Mixing modes source: 31 “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)”

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Janam Jhaveri Phonons Phonon Calculations 33 Optional: select whether to perform phonon calculations

Janam Jhaveri Phonons Calculation type 34 Select whether to perform dispersion relationship or a single q-point calculation

Janam Jhaveri Phonons Atomic Mass 35 Enter list of atom types and their mass in amu (format shown below) Format: Atom symbol mass … Format: Atom symbol mass …

Janam Jhaveri Phonons Convergence criterion 36 Enter energy value as phonon convergence criterion. Note energy is given in Ry.

Janam Jhaveri Phonons Dielectric constant 37 Optional: choose to calculate macroscopic dielectric constant Warning: will not work with metallic systems Optional: choose to calculate macroscopic dielectric constant Warning: will not work with metallic systems

Janam Jhaveri Phonons Q-grid spacing 38 If you’re doing a dispersion relationship calculation, select number of q-points to be used in the x, y and z- direction 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 Phonons Dispersion curve path 39 If you’re doing a dispersion relationship calculation, select high symmetry points (Q- points) for the path. Q-points should be given in fractional (reduced) coordinates. If you’re doing a dispersion relationship calculation, select high symmetry points (Q- points) for the path. Q-points should be given in fractional (reduced) coordinates.

Janam Jhaveri Phonons Number of points 40 Enter number of points on dispersion curve path

Janam Jhaveri Phonons Single q-point 41 If you’re doing a single Q- point calculation, choose Q- point on which to do phonon calculations If you’re doing a single Q- point calculation, choose Q- point on which to do phonon calculations

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Janam Jhaveri Band structure Band structure Calculations 43 Optional: select whether to perform band structure calculations

Janam Jhaveri Band structure Band structure path 44 Select high symmetry points (K-points) along which the path should be plotted. K-points should be given in fractional (reduced) coordinates. Select high symmetry points (K-points) along which the path should be plotted. K-points should be given in fractional (reduced) coordinates.

Janam Jhaveri Band structure Number of points on path 45 Enter number of points on band structure path

Janam Jhaveri Density of States Minimum Energy 46 Enter minimum of energy grid to plot. Note energy is given in eV.

Janam Jhaveri Density of States Maximum Energy 47 Enter maximum of energy grid to plot

Janam Jhaveri Density of States Energy grid step 48 Enter energy grid step to plot

Janam Jhaveri References