dft calculations with quantum espresso: user guide
DESCRIPTION
DFT Calculations with Quantum Espresso: User Guide. Janam Jhaveri Network for Computational Nanotechnology (NCN) Electrical and Computer Engineering [email protected] 02/07/2011. Getting Started. Quick Run: DOS and Band Structure Silicon. Quick Initial Run. - PowerPoint PPT PresentationTRANSCRIPT
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
02/07/2011
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Quick Initial Run
Hit ‘Simulate’ and wait for results
4
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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
8
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
9
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
10
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
11
Simple Cubic (cubic P) Face-Centered Cubic (cubic F)
http://en.wikipedia.org/wiki/Crystal_structure
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Input Geometry
Structure types
12
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
13
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
14
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
15
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
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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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
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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 http://www.pwscf.org/pseudo.php
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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
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Energy Expression
K-grid
21
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
23
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
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
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Energy Expression
Gaussian Spreading
26
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
27
“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
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”
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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
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Energy Expression
Mixing factor
30
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
33
Optional: select whether to perform phonon calculationsOptional: select whether to
perform phonon calculations
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Phonons
Calculation type
34
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
35
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
36
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
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
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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
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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.
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Phonons
Number of points
40
Enter number of points on dispersion curve path
Enter number of points on dispersion curve path
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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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Band structure
Band structure Calculations
43
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
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.
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Band structure
Number of points on path
45
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
46
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
48
Enter energy grid step to plotEnter energy grid step to plot
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References
49
• 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