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 Presentation
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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)
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
Janam Jhaveri 6
Janam Jhaveri 7
Janam Jhaveri
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
Janam Jhaveri
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
Body-Centered Cubic (cubic I) Hexagonal (Hexagonal and Trigonal P)
http://en.wikipedia.org/wiki/Crystal_structure
Janam Jhaveri
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…
Janam Jhaveri
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
Janam Jhaveri
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
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
Janam Jhaveri 17
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 http://www.pwscf.org/pseudo.php
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
Select number of k-points to be used in the x, y and z-
direction
Janam Jhaveri
Energy Expression
Bands
22
Select number of bandsSelect number of bands
Janam Jhaveri
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
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
If Occupation selected is ‘smearing’, enter a value for
tetrahedra: for calculation of DOS in metals (see PRB49, 16223 (1994)) Not suitable (because not variational) for force/optimization/dynamics calculations