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 JhaveriNetwork for Computational Nanotechnology (NCN)

Electrical and Computer Engineering

jjhaver@purdue.edu

02/07/2011

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Quick Initial Run

Hit ‘Simulate’ and wait for results

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Quick Initial Run

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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

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Optional: Select whether to upload input geometry or use a

pre-made structure

Optional: Select whether to upload input geometry or use a

pre-made structure

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Input Geometry

Atomic Coordinates

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Select whether to use Cartesian or Fractional 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

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Input Geometry

Structure Type

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Select structure type

See p.11-12 for more info

Select structure type

See p.11-12 for more info

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Input Geometry

Structure types

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Simple Cubic (cubic P) Face-Centered Cubic (cubic F)

http://en.wikipedia.org/wiki/Crystal_structure

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Input Geometry

Structure types

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Body-Centered Cubic (cubic I) Hexagonal (Hexagonal and Trigonal P)

http://en.wikipedia.org/wiki/Crystal_structure

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Input Geometry

Atomic Coordinates

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Enter structure (format shown below)

Enter structure (format shown below)

Format:Number of atomsInformation about structureAtom symbol coordinate 1 coordinate 2 coordinate 3Atom symbol coordinate 1 coordinate 2 coordinate 3…

Format:Number of atomsInformation about structureAtom symbol coordinate 1 coordinate 2 coordinate 3Atom symbol coordinate 1 coordinate 2 coordinate 3…

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Input Geometry

Cell Vectors

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If structure type chosen is ‘Determine unitcell (free)’, enter

cell vectors

If structure type chosen is ‘Determine unitcell (free)’, enter

cell vectors

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Input Geometry

Lattice Parameter a

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If structure type chosen is NOT ‘Determine unitcell (free)’, enter

lattice parameter a

See p. 11-13 for definition of 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

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Input Geometry

Lattice Parameter c

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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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Energy Expression

Functional

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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

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Energy Expression

Exchange-correlation energies

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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

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Energy Expression

Relax

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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

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Energy Expression

K-grid

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Select number of k-points to be used in the x, y and z-

direction

Select number of k-points to be used in the x, y and z-

direction

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Energy Expression

Bands

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Select number of bandsSelect number of bands

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Energy Expression

Energy cutoffs

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Select energy cutoffs and self-consistent field (SCF) convergence criterion

Select energy cutoffs and self-consistent field (SCF) convergence criterion

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Energy Expression

Occupation Options

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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

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Energy Expression

Smearing

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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

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Energy Expression

Gaussian Spreading

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If Occupation selected is ‘smearing’, enter a value for

the Gaussian spreading/broadening

If Occupation selected is ‘smearing’, enter a value for

the Gaussian spreading/broadening

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Energy Expression

Occupation Optionssource: http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3900903

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“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“

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Energy Expression

Smearing Optionssource: http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3900938

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“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”

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Energy Expression

Mixing Options

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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

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Energy Expression

Mixing factor

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Enter a value for the mixing factor

Enter a value for the mixing factor

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Energy Expression

Mixing modessource: http://www.quantum-espresso.org/input-syntax/INPUT_PW.html#id3901509

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“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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Phonons

Phonon Calculations

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Optional: select whether to perform phonon calculationsOptional: select whether to

perform phonon calculations

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Phonons

Calculation type

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Select whether to perform dispersion relationship or a single q-point calculation

Select whether to perform dispersion relationship or a single q-point calculation

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Phonons

Atomic Mass

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Enter list of atom types and their mass in amu (format

shown below)

Enter list of atom types and their mass in amu (format

shown below)

Format:Atom symbol massAtom symbol mass…

Format:Atom symbol massAtom symbol mass…

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Phonons

Convergence criterion

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Enter energy value as phonon convergence criterion. Note

energy is given in Ry.

Enter energy value as phonon convergence criterion. Note

energy is given in Ry.

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Phonons

Dielectric constant

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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

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Phonons

Q-grid spacing

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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

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Phonons

Dispersion curve path

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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.

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Phonons

Number of points

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Enter number of points on dispersion curve path

Enter number of points on dispersion curve path

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Phonons

Single q-point

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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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Band structure

Band structure Calculations

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Optional: select whether to perform band structure

calculations

Optional: select whether to perform band structure

calculations

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Band structure

Band structure path

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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.

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Band structure

Number of points on path

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Enter number of points on band structure path

Enter number of points on band structure path

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Density of States

Minimum Energy

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Enter minimum of energy grid to plot. Note energy is given in

eV.

Enter minimum of energy grid to plot. Note energy is given in

eV.

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Density of States

Maximum Energy

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Enter maximum of energy grid to plot

Enter maximum of energy grid to plot

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Density of States

Energy grid step

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Enter energy grid step to plotEnter energy grid step to plot

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References

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• 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