1. Introduction to Quantum Espresso
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2. ESPRESSO
ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation and Optimization
QE is an integrated suite of computer codes for electronic-structure calculations and material modeling, based on DFT, Plane waves, & Pseudopotential (numerical trick, replace nuclear potential by pseudopotential)
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3. The QE Project The two main goals of this project are:
to foster methodological innovation in the field of electronic-structure simulations
To provide a wide and diverse community of end users with hightly efficient, robust, and userfriendly software implementing the most recent innovations in this field.
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4. The QE Project
Applications are run through text input files based on fortran namelists
The QE distribution is written, mostly in Fortran-95, with some part in C or in Fortran-77
Parallelization via standard MPI libraries.
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5. Code
The codes are constructed around the use of periodic boundary conditions
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6. Simulations
Calculation of the Kohn-Sham (KS) orbitals and energies for isolated or extended periodic system, and their ground-state energy
Complete structural optimizations of the microscopic (atomic coordinates) and macroscopic (unit cell) degrees of freedom, using Hellmann-Feynman forces and stresses
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7. Simulations
Ground state of magnetic or spin-polarized system, including spin-orbit coupling and non collinear magnetism
ab initio molecular dynamics (MD), using either the Car-Parrinello Lagrangian or the Hellmann-Feynman forces calculated on the Born-Oppenheimer surface, in variety of thermodynamical ensembles, including NPT variable-cell MD
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8. Simulations
Density-functional peturbation theory (DFPT), to calculate second and third derivatives of the total energy at any arbitrary wavelength, providing phonon dispersions, electron-phonon and phonon-phonon interactions, and static response functions (dielectric tensors, Born effective charges, IR spectra, and Raman tensors)
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9. Simulations
Location of saddle points and transition states via transition-path optimization using the nudged elastic band (NEB) method
Ballistic conductance within the Landauer-Buttiker theory using the scattering approach
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10. Simulations
Generation of maximally localized Wannier functions and related quantities
Calculation of nuclear magnetic resonance (NMR) and electronic paramagnetic resonance (EPR) parameters
Calculation of K-edge x-ray absorption spectra.
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11. Data file format Data files should ideally be:
Extensible
Self-documenting
Efficient
Structured file formats, notably Hierarchical Data Format (HDF) and network Common Data Form (netCDF), that have been widely used for years in other communities
File formats based on the Extensible Markup Language (XML)
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12. QE Packages The current version (4.1) includes:
lines of fortran-90/95 code,
1000 lines of fortran-77 code,
1000 lines of C code,
30000 lines of Tcl code + external standard math libraries such as FFTW (Fast Fourier-Transform Package), BLAS (BASIC Linear Algebra Subroutine), LAPACK (Linear Algebra Package), & external toolkit iotk
There are lines of specific documentation, 100 different examples & +100 tests of the different functionalities.
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13. QE Packages PWscf CP PHonon Atomic PWcond GIPAW XPECTRA Wannier90
PostProc
Pwgui
We’ll mostly deal with PWSCF. Other components have similar input structure
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14. QE Packages PWscf (Plane-Wave Self-Consistent Field)
We will use this to perform total energy calculations
Density-functional & Hartree-Fock calculations of the energy electronic structure
Phonon dispersion curves, dielectric constants, & Born effective charges
PWSCF uses both norm-conserving pseudopotentials (PP), ultrasoft pseudopotential (US-PP) & projector augmented wave (PAW) potentials within DFT
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15. QE Packages CP (Car-Parrinello molecular dynamics)
The CP code is the specialized module performing Car–Parrinello ab initio MD.
the electron density is augmented through a Fourier interpolation scheme in real space (‘box grid’) that is particularly efficient for large-scale calculations.
CP implements the same functionals as PWscf,with the exception of hybrid functionals; a simplified one-electron self-interaction correction (SIC) is also available.
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16. QE Packages CP (Car-Parrinello molecular dynamics)
CP can also be used to directly minimize the electronic energy functional to self-consistency while keeping thenuclei fixed, or to perform structural minimizations of nuclear positions, using the ‘global minimization’ approaches of and damped dynamics or conjugate-gradients on the electronic or ionic degrees of freedom.
CP can perform NEB and metadynamics calculations
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17. QE Packages
PHonon
The PHonon package implements density-functional perturbation theory (DFPT) for the calculation of second- and third-order derivatives of the energy with respect to atomic displacements and to electric fields
Advanced features of the PHonon package include the calculation of third-order energy derivatives and of electron–phonon or phonon–phonon interaction coefficients
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18. QE Packages
Atomic
The atomic code performs three different tasks (These three tasks can be either separately executed or performed in a single run):
Solution of the self-consistent all-electron radial KS equations (with a Coulomb nuclear potential and spherically symmetric charge density)
generation of NC PPs, US PPs, or PAW datasets
test of the above PPs and data-sets.
Three different all-electron equations are available:
The nonrelativistic radial KS equations
the scalar relativistic approximation to the radial Dirac equations
The radial Dirac-like equations derived within relativistic densityfunctional theory
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19. QE Packages
PWcond
The PWcond code implements the scattering approach proposed by Choi and Ihm for the study of coherent electron transport in atomic-sized nanocontacts within the Landauer–B¨uttiker theory
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20. QE Packages
GIPAW
The GIPAW code allows for the calculation of physical parameters measured in:
NMR spectroscopy in insulators (the electric-field-gradient (EFG) tensors and the chemical shift tensors)
EPR spectroscopy for paramagnetic defects in solids or in radicals (the hyperfine tensors and the gtensor).
The code also computes the magnetic susceptibility of nonmagnetic insulators
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21. QE Packages
XSPECTRA
The XSPECTRA code allows for the calculation of K-edge x-ray absorption spectra (XAS).
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22. QE Packages
Wannier90
Wannier90 is a code that calculates maximally localizedWannier functions in insulators or metals, a number of properties that can be conveniently expressed in a Wannier basis.
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23. QE Packages
PostProc
The PostProc module contains a number of codes for postprocessing and analysis of data files produced by PWscf and CP
The following operations can be performed:
Interfacing to graphical and molecular graphics applications
Interfaces to other codes that use DFT results from QE for further calculations
Calculation of various quantities that are useful for the analysis of the results.
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24. QE Packages
PWgui
PWgui is the graphical user interface (GUI) for the PWscf, PHonon, and atomic packages as well as for some of the main codes in PostProc
PWgui is an input file builder whose main goal is to lower the learning barrier for the newcomer, who would otherwise have to struggle with the input syntax
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25. Parallelization
High performance on massively parallel architectures is achieved by distributing both data and computations in a hierarchical way across available processors
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26. Parallelization
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27. Parallelization Image parallelization pool parallelization
by dividing processors into nimage groups, each taking care of one or more images
pool parallelization
by dividing each group of processors into npool pools of processors, each taking care of one or more k-points
plane-wave parallelization
by distributing real- and reciprocal-space grids across the nPW processors of each pool.
Task group parallelization
in which processors are divided into ntask task groups of nFFT = nPW/ntask processors, each one taking care of different groups of electron states to be Fourier transformed, while each FFT is parallelized inside a task group
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28. General Structure Namelist-calculation specifications
&CONTROL: general variables controlling the run
&SYSTEM: structural information on the system under investigation
&ELECTRONS: electronic variables
&IONS (optional): ionic variables
&CELL (optional): variable-cell dynamics
&PHONON (optional): information required to produce data for
phonon calculations
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29. General Structure Nonoptional & optional cards ATOMIC SPECIES
ATOMIC POSITIONS
K POINTS
CELL PARAMETERS(optional)
OCCUPATIONS(optional)
FIRST IMAGE(optional)
LAST IMAGE(optional)
CLIMBING IMAGES(optional)
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30. Typical input file – diamond Si

31. The namelist &control calculation restart_mode
scf: single point calculation without geometric optimization
nscf : non-self-consistent calculation
relax : geometric optimization
md : molecular dynamics
vc-relax : geometric optimization with variable unit cell coordinates
restart_mode
from scratch : Start from an initial guess
restart : Start from earlier data
outdir: Directory where intermediates are dumped.
pseudo_dir: Directory where the pseudopotentials live.
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32. The namelist &system nat : number of atoms
ntyp : number of types of atoms
nbnd : number of states to be calculated (unoccupied states as well)
ecutwfc : kinetic energy cutoff (for planewaves)
ecutrho : density cutoff (for the augmentation charge in USPP ≈ 10× ecutwfc)
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33. The namelist &system
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34. The namelist &system
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35. The namelist &system
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36. The namelist &electrons
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37. The namelist &ions
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38. Cards
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39. Cards
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40. THANK YOU
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41. References
Paolo Giannozzi et al 2009 J. Phys.: Condens. Matter doi: / /21/39/395502
Ustunel, Hande 2007 Quantum-Espresso
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