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
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Quick Initial Run
Hit ‘Simulate’ and wait for results
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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
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Input Geometry
Atomistic Structure
Optional: Select whether to
upload input geometry or use a
pre-made structure
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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
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Input Geometry
Structure Type
Select structure type
See p.11-12 for more info
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Input Geometry
Structure types
Simple Cubic (cubic P)
Face-Centered Cubic (cubic F)
http://en.wikipedia.org/wiki/Crystal_structure
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Input Geometry
Structure types
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
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
…
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Input Geometry
Cell Vectors
If structure type chosen is
‘Determine unitcell (free)’, enter
cell vectors
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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
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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
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Energy Expression
Functional
Select either LDA or GGA
(PBE) for ExchangeCorrelation functional
See p. 19 for more info
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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
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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
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Energy Expression
K-grid
Select number of k-points to
be used in the x, y and zdirection
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Energy Expression
Bands
Select number of bands
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Energy Expression
Energy cutoffs
Select energy cutoffs and selfconsistent field (SCF)
convergence criterion
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Energy Expression
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
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
If Occupation selected is
‘smearing’, enter a value for
the Gaussian
spreading/broadening
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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“
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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”
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Energy Expression
Mixing Options
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
Enter a value for the mixing
factor
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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)”
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Phonons
Phonon Calculations
Optional: select whether to
perform phonon calculations
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Phonons
Calculation type
Select whether to perform
dispersion relationship or a
single q-point calculation
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Phonons
Atomic Mass
Enter list of atom types and
their mass in amu (format
shown below)
Format:
Atom symbol mass
Atom symbol mass
…
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Phonons
Convergence criterion
Enter energy value as phonon
convergence criterion. Note
energy is given in Ry.
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Phonons
Dielectric constant
Optional: choose to calculate
macroscopic dielectric
constant
Warning: will not work with
metallic systems
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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
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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.
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Phonons
Number of points
Enter number of points on
dispersion curve path
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Phonons
Single q-point
If you’re doing a single Qpoint calculation, choose Qpoint on which to do phonon
calculations
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Band structure
Band structure Calculations
Optional: select whether to
perform band structure
calculations
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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.
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Band structure
Number of points on path
Enter number of points on
band structure path
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Density of States
Minimum Energy
Enter minimum of energy grid
to plot. Note energy is given in
eV.
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Density of States
Maximum Energy
Enter maximum of energy grid
to plot
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Density of States
Energy grid step
Enter energy grid step to plot
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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
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