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Developer's Manual for QUANTUM ESPRESSO(v. 4.3.1)


Contents

1 Introduction

1.1 Who should read (and who should write) this guide

The intended audience of this guide is everybody who wants to:

The same category of people should also write this guide, of course.

1.2 Who may read this guide but will not necessarily profit from it

People who want to know about the capabilities of QUANTUM ESPRESSO, or who want just to use it, should read the User Guide.

People who want to know about the methods or the physics behind QUANTUM ESPRESSO should read first the relevant literature (some pointers in the User Guide).

1.3 How to contribute to QUANTUM ESPRESSO

You can contribute to a better QUANTUM ESPRESSO, even if you are not a full-fledged developer, by

1.4 How to make major contributions to QUANTUM ESPRESSO

If you want to get involved as a developer and contribute serious or nontrivial stuff, you should register for the QUANTUM ESPRESSO project on qe-forge.org. You may also consider the idea of opening your own project on qe-forge.org. There is a developers' mailing list, q-e-developers, to which you should subscribe, and a mailing list receiving commit message, q-e-commits. The ideal procedure to add extensive changes is as follows:

1.5 About qe-forge.org

qe-forge.org is the portal for QUANTUM ESPRESSO developers, contributors, and for anybody else wanting to develop a project in the field of atomistic simulations. qe-forge.org provides a CVS or SVN repository, mailing lists, a wiki, upload space, a bug tracking facility, various other tools that are useful for developers. You can use either CVS or SVN but not both together. Note that the usage of the wiki provided by qe-forge.org is currently disabled for security reasons.

You can open your own project, retaining all rights on it (including the right not to release anything); or else, you can register as a developer in an existing project (or both).

Currently QUANTUM ESPRESSO uses the following development tools:

Everybody is encouraged to explore other capabilities of qe-forge.org.

Once you are registered, you need to register your SSH keys in order to have read-write access the CVS or SVN repository (if you have been allowed by the project leader). The procedure is as follows:

Specific to the QUANTUM ESPRESSO project:

1.6 Hints, Caveats, Do's and Dont's for developers

When you modify the program sources, run the install/makedeps.sh script or type make depend to update files make.depend in the various subdirectories.


1.7 Guidelines for reporting bugs

2 Structure of the distribution

2.0.1 Libraries

Subdirectory flib/ contains libraries written in fortran77 (*.f) and in fortran-90 (*.f90). The latter should not depend on any module, except for modules kinds and constants.

Subdirectory clib/ contains libraries written in C (*.c). Functions that are called by fortran should be preprocessed using the macros:

  1. F77_FUNC (func,FUNC) for function func, not containing underscore(s) in name
  2. F77_FUNC_(f_nc,F_NC) for function f_nc, containing underscore(s) in name
These macros are defined in file include/c_defs.h. This file must be included by all *.c files. The macros are automagically generated by configure and choose the correct case (lowercase or uppercase) and the correct number of final underscores. See file include/defs.h.README for more info.

2.1 Installation mechanism

The code contains C-style preprocessing directives. There are two ways to do preprocessing of fortran files:

In the first case, one needs to specify in the make.sys file the fortran compiler option that tells the compiler to pre-process first. In the second case, one needs to specify the C precompiler and options (if needed) in make.sys. Normally, configure should take care of this.

2.1.1 How to edit the configure script

The configure script is generated from its source file configure.ac by the GNU autocon utility (http://www.gnu.org/software/autoconf/). Don't edit configure directly: whenever it gets regenerated, your changes will be lost. Instead, go to the install/ directory, edit configure.ac, then run autocon to regenerate configure. If you want to keep the old configure, make a copy first.

GNU autocon is installed by default on most Unix/Linux systems. If you don't have it on your system, you'll have to install it. You will need a recent version (e.g. v.2.65) of autocon, because our configure.ac file uses recent syntax.

configure.ac is a regular Bourne shell script (i.e., "sh" - not csh!), except that:

-
capitalized names starting with "AC_" are autocon macros. Normally you shouldn't have to touch them.
-
square brackets are normally removed by the macro processor. If you need a square bracket (that should be very rare), you'll have to write two.

You may refer to the GNU autocon Manual for more info.

make.sys.in is the source file for make.sys, that configure generates: you might want to edit that file as well. The generation procedure is as follows: if configure.ac contains the macro "AC_SUBST(name)", then every occurrence of "@name@" in the source file will be substituted with the value of the shell variable "name" at the point where AC_SUBST was called.

Similarly, configuremsg is generated from configure.msg.in: this file is only used by configure to print its final report, and isn't needed for the compilation. We did it this way so that our configure may also be used by other projects, just by replacing the QUANTUM ESPRESSO-specific configure.msg.in by your own.

configure writes a detailed log of its operation to "config.log". When any configuration step fails, you may look there for the relevant error messages. Note that it is normal for some checks to fail.

2.1.2 How to add support for a new architecture

In order to support a previously unsupported architecture, first you have to figure out which compilers, compilation flags, libraries etc. should be used on that architecture. In other words, you have to write a make.sys that works: you may use the manual configuration procedure for that (see the User Guide). Then, you have to modify configure so that it can generate that make.sys automatically.

To do that, you have to add the case for your architecture in several places throughout configure.ac:

  1. Detect architecture

    Look for these lines:

      if test "$arch" = ""
      then
              case $host in
                      ia64-*-linux-gnu )      arch=ia64   ;;
                      x86_64-*-linux-gnu )    arch=x86_64 ;;
                      *-pc-linux-gnu )        arch=ia32   ;;
                      etc.
    
    Here you must add an entry corresponding to your architecture and operating system. Run config.guess to obtain the string identifying your system. For instance on a PC it may be "i686-pc-linux-gnu", while on IBM SP4 "powerpc-ibm-aix5.1.0.0". It is convenient to put some asterisks to account for small variations of the string for different machines of the same family. For instance, it could be "aix4.3" instead of "aix5.1", or "athlon" instead of "i686"...

  2. Select compilers

    Look for these lines:

      # candidate compilers and flags based on architecture
      case $arch in
      ia64 | x86_64 )
            ...
      ia32 )
            ...
      aix )
            ...
      etc.
    

    Add an entry for your value of $arch, and set there the appropriate values for several variables, if needed (all variables are assigned some reasonable default value, defined before the "case" block):

    - "try_f90" should contain the list of candidate Fortran 90 compilers, in order of decreasing preference (i.e. configure will use the first it finds). If your system has parallel compilers, you should list them in "try_mpif90".

    - "try_ar", "try_arflags": for these, the values "ar" and "ruv" should be always fine, unless some special flag is required (e.g., -X64 With sp4).

    - you should define "try_dflags" if there is any "#ifdef" specific to your machine: for instance, on IBM machines, "try_dflags=-D__AIX" . A list of such flags can be found in file include/defs.h.README.

    You shouldn't need to define the following: - "try_iflags" should be set to the appropriate "-I" option(s) needed by the preprocessor or by the compiler to locate *.h files to be included; try_iflags="-I../include" should be good for most cases

    For example, here's the entry for IBM machines running AIX:

       aix )
            try_mpif90="mpxlf90_r mpxlf90"
            try_f90="xlf90_r xlf90 $try_f90"
            try_arflags="-X64 ruv"
            try_arflags_dynamic="-X64 ruv"
            try_dflags="-D__AIX -D__XLF"
            ;;
    
    The following step is to look for both serial and parallel fortran compilers:
      # check serial Fortran 90 compiler...
      ...
      AC_PROG_F77($f90)
      ...
            # check parallel Fortran 90 compiler
      ...
            AC_PROG_F77($mpif90)
      ...
      echo setting F90... $f90
      echo setting MPIF90... $mpif90
    
    A few compilers require some extra work here: for instance, if the Intel Fortran compiler was selected, you need to know which version because different versions need different flags.

    At the end of the test,

    - $mpif90 is the parallel compiler, if any; if no parallel compiler is found or if -disable-parallel was specified, $mpif90 is the serial compiler

    - $f90 is the serial compiler

    Next step: the choice of (serial) C and Fortran 77 compilers. Look for these lines:

      # candidate C and f77 compilers good for all cases
      try_cc="cc gcc"
      try_f77="$f90"
    
      case "$arch:$f90" in
      *:f90 )
            ....
      etc.
    
    Here you have to add an entry for your architecture, and since the correct choice of C and f77 compilers may depend on the fortran-90 compiler, you may need to specify the f90 compiler as well. Again, specify the compilers in try_cc and try_f77 in order of decreasing preference. At the end of the test,

    - $cc is the C compiler

    - $f77 is the Fortran 77 compiler, used to compile *.f files (may coincide with $f90)

  3. Specify compilation flags.

    Look for these lines:

      # check Fortran compiler flags
      ...
      case "$arch:$f90" in
      ia64:ifort* | x86_64:ifort* )
            ...
      ia64:ifc* )
            ...
      etc.
    
    Add an entry for your case and define:

    - "try_fflags": flags for Fortran 77 compiler.

    - "try_f90flags": flags for Fortran 90 compiler. In most cases they will be the same as in Fortran 77 plus some others. In that case, define them as "$(FFLAGS) -something_else".

    - "try_fflags_noopt": flags for Fortran 77 with all optimizations turned off: this is usually "-O0". These flags must be used for compiling flib/dlamch.f (part of our version of Lapack): it won't work properly with optimization.

    - "try_ldflags": flags for the linking phase (not including the list of libraries: this is decided later).

    - "try_ldflags_static": additional flags to select static compilation (i.e., don't use shared libraries).

    - "try_dflags": must be defined if there is in the code any #ifdef specific to your compiler (for instance, -D__INTEL for Intel compilers). Define it as "$try_dflags -D..." so that pre-existing flags, if any, are preserved.

    - if the Fortran 90 compiler is not able to invoke the C preprocessor automatically before compiling, set "have_cpp=0" (the opposite case is the default). The appropriate compilation rules will be generated accordingly. If the compiler requires that any flags be specified in order to invoke the preprocessor (for example, "-fpp " - note the space), specify them in "pre_fdflags".

    For example, here's the entry for ifort on Linux PC:

      ia32:ifort* )
              try_fflags="-O2 -tpp6 -assume byterecl"
              try_f90flags="\$(FFLAGS) -nomodule"
              try_fflags_noopt="-O0 -assume byterecl"
              try_ldflags=""
              try_ldflags_static="-static"
              try_dflags="$try_dflags -D__INTEL"
              pre_fdflags="-fpp "
              ;;
    
    Next step: flags for the C compiler. Look for these lines:
      case "$arch:$cc" in
      *:icc )
            ...
      *:pgcc )
            ...
      etc.
    
    Add an entry for your case and define:

    - "try_cflags": flags for C compiler.

    - "c_ldflags": flags for linking, when using the C compiler as linker. This is needed to check for libraries written in C, such as FFTW.

    - if you need a different preprocessor from the standard one ($CC -E), define it in "try_cpp".

    For example for XLC on AIX:

      aix:mpcc* | aix:xlc* | aix:cc )
              try_cflags="-q64 -O2"
              c_ldflags="-q64"
              ;;
    
    Finally, if you have to use a nonstandard preprocessor, look for these lines:
      echo $ECHO_N "setting CPPFLAGS... $ECHO_C"
      case $cpp in
            cpp) try_cppflags="-P -traditional" ;;
            fpp) try_cppflags="-P"              ;;
            ...
    
    and set "try_cppflags" as appropriate.

  4. Search for libraries

    To instruct configure to search for libraries, you must tell it two things: the names of libraries it should search for, and where it should search.

    The following libraries are searched for:

    - BLAS or equivalent. Some vendor replacements for BLAS that are supported by QUANTUM ESPRESSO are:

    MKL on Linux, 32- and 64-bit Intel CPUs
    ACML on Linux, 64-bit AMD CPUs
    essl on AIX
    SCSL on sgi altix
    SUNperf on sparc
    Moreover, ATLAS is used over BLAS if available.

    - LAPACK or equivalent. Some vendor replacements for LAPACK that are supported by QUANTUM ESPRESSO are:

    mkl on linux SUNperf on sparc

    - FFTW (version 3) or another supported FFT library. The latter include:

    essl on aix ACML on Linux, 64-bit AMD CPUs SUNperf on sparc

    - the MASS vector math library on aix

    - an MPI library. This is often automatically linked by the compiler

    If you have another replacement for the above libraries, you'll have to insert a new entry in the appropriate place.

    This is unfortunately a little bit too complex to explain. Basic info: "AC_SEARCH_LIBS(function, name, ...)" looks for symbol "function" in library "libname". If that is found, "-lname" is appended to the LIBS environment variable (initially empty). The real thing is more complicated than just that because the "-Ldirectory" option must be added to search in a nonstandard directory, and because a given library may require other libraries as prerequisites (for example, Lapack requires BLAS).

3 Algorithms

3.1 Gamma tricks

In calculations using only the $ \Gamma$ point (k=0), the Kohn-Sham orbitals can be chosen to be real functions in real space, so that $ \psi$(G) = $ \psi^{*}_{}$(- G). This allows us to store only half of the Fourier components. Moreover, two real FFTs can be performed as a single complex FFT. The auxiliary complex function $ \Phi$ is introduced: $ \Phi$(r) = $ \psi_{j}^{}$(r) + i$ \psi_{{j+1}}^{}$(r) whose Fourier transform $ \Phi$(G) yields

$ \psi_{j}^{}$(G) = $ {\Phi(G) + \Phi^*(G)\over 2}$,$ \psi_{{j+1}}^{}$(G) = $ {\Phi(G) - \Phi^*(G)\over 2i}$.

A side effect on parallelization is that G and - G must reside on the same processor. As a consequence, pairs of columns with Gn'1, n'2, n'3 and G-n'1,-n'2, n'3 (with the exception of the case n'1 = n'2 = 0 ), must be assigned to the same processor.

4 Structure of the code


4.1 Preprocessing

The code contains C-style preprocessing directives. Most fortran compilers directly support them; some don't, and preprocessing is ''hand-made'' by the makefile using the C preprocessor cpp. The C preprocessor may: The file include/defs.h.README contains a list of definitions that are used in the code. In order to make preprocessing options easy to see, preprocessing variables should start with two underscores, as __expression in the above example. Traditionally ''preprocessed'' variables are also written in uppercase.

5 Parallelization

In parallel execution, PW starts N independent processes (do not start more than one per processor!) that communicate via calls to MPI libraries. Each process has its own set of variables and knows nothing about other processes' variables. Variables that take little memory are replicated, those that take a lot of memory (wavefunctions, G-vectors, R-space grid) are distributed.

Beware: replicated calculations may either be performed independently on each processor, or performed on one processor and broadcast to all others. The first approach requires less programming, but it is unsafe: in principle all processors should yield exactly the same results, if they work on the same data, but sometimes they don't (depending on the machine, compiler, and libraries). Even a tiny difference in the last significant digit can eventually cause serious trouble if allowed to build up, especially when a replicated check is performed (in which case the code may ''hang'' if the check yields different results on different processors). Never assume that the value of a variable produced by replicated calculations is exactly the same on all processors: when in doubt, broadcast the value calculated on a specific processor (the ''root'' processor) to all others.

5.1 Paradigms

5.2 Implementation

5.2.1 Data distribution

Quantum ESPRESSO employ arrays whose memory requirements fall into three categories.

6 File Formats

6.1 Data file(s)

QUANTUM ESPRESSO restart file specifications: Paolo Giannozzi scripsit AD 2005-11-11, Last modified by Andrea Ferretti 2006-10-29

6.1.1 Rationale

Requirements: the data file should be

Solutions: Integration with other packages:

6.1.2 General structure

Format name: '''QEXML'''
Format version: '''1.4.0'''

The "restart file" is actually a "restart directory", containing several files and sub-directories. For CP/FPMD, the restart directory is created as "$prefix_$ndw/", where $prefix is the value of the variable "prefix". $ndw the value of variable ndw, both read in input; it is read from "$prefix_$ndr/", where $ndr the value of variable ndr, read from input. For PWscf, both input and output directories are called "$prefix.save/".

The content of the restart directory is as follows:

    ''data-file.xml''          which contains:
                               - general information that doesn't require large data set: 
                                 atomic structure, lattice, symmetries, parameters of the run, ...
                               - pointers to other files or directories containing bulkier data:
                                 such as grids, wavefunctions, charge density, potentials, ...
      
    ''charge_density.dat''     contains the charge density
    ''spin_polarization.dat''  contains the spin polarization (rhoup-rhodw) (LSDA calculations)
    ''magnetization.x.dat''    
    ''magnetization.y.dat''    contain the spin polarization along x,y,z (noncollinear calculations)  
    ''magnetization.z.dat'' 
    ''lambda.dat''             contains occupations (Car-Parrinello dynamics only
    ''mat_z.1''                contains occupations (ensemble-dynamics only)
    
    <pseudopotentials>     A copy of all pseudopotential files given in input
    
    <k-point dirs>         One or more subdirectories ''K00001/'', ''K00002/'', etc, one per k-point.
Each k-point directory contains:
    ''evc.dat''                containing the wavefunctions for spin-unpolarized calculations, OR
    ''evc1.dat''
    ''evc2.dat''               containing the spin-up and spin-down wavefunctions, respectively, 
                           for spin polarized (LSDA) calculations;
  
                           in a molecular dynamics run, also wavefunctions at the preceding time step:
    ''evcm.dat''               for spin-unpolirized calculations OR
    ''evcm1.dat''
    ''evcm2.dat''              for spin polarized calculations;
     
    ''gkvectors.dat''          with the details of specific k+G grid;
    ''eigenval.xml''           containing the eigenvalues for the corresponding k-point for spin-unpolarized calculations, OR
    ''eigenval1.xml''      
    ''eigenval2.xml''          for spin-polarized calculations;

6.1.3 Structure of file "data-file.xml"

* ''XML Header'': whatever is needed to have a well-formed XML file

* ''Body'': introduced by <Root>, terminated by </Root>. Contains first-level tags only. These contain only other tags, not values. XML syntax applies.

* ''First-level tags'': contain either
** second-level tags
** "data tags": tags containing data (values for a given variable)
** "file tags": tags pointing to a file

''data tags syntax'' ( [...] = optional ) :
      <TAG type="vartype" size="n" [UNIT="units"] [LEN="k"]>
      values (in appropriate units) for variable corresponding to TAG:
      n elements of type vartype (if character, of lenght k)
      </TAG>
where TAG describes the variable into which data must be read;<br>
"vartype" may be "integer", "real", "character", "logical";<br>
if type="logical", LEN=k" must be used to specify the length
of the variable character; size="n" is the dimension.<br>
Acceptable values for "units" depend on the specific tag.

''Short syntax'', used only in a few cases:
      <TAG attribute="something"/> . 
For instance:
      <FFT_GRID nr1="NR1" nr2="NR2" nr3="NR3"/>
defines the value of the FFT grid parameters nr1, nr2, nr3
for the charge density

6.1.4 Sample

* Header:

 <?xml version="1.0"?>
 <?iotk version="1.0.0test"?>
 <?iotk file_version="1.0"?>
 <?iotk binary="F"?> 

These are meant to be used only by iotk (actually they aren't)

* First-level tags:

  - <HEADER>         (global information about fmt version)
  - <CONTROL>        (miscellanea of internal information)
  - <STATUS>         (information about the status of the CP simulation)
  - <CELL>           (lattice vector, unit cell, etc)
  - <IONS>           (type and positions of atoms in the unit cell etc)
  - <SYMMETRIES>     (symmetry operations)
  - <ELECTRIC_FIELD> (details for an eventual applied electric field)
  - <PLANE_WAVES>    (basis set, cutoffs etc)
  - <SPIN>           (info on spin polarizaztion)
  - <MAGNETIZATION_INIT>     (info about starting or constrained magnetization)
  - <EXCHANGE_CORRELATION>
  - <OCCUPATIONS>    (occupancy of the states)
  - <BRILLOUIN_ZONE> (k-points etc)
  - <PHONON>         (info for phonon calculations)  
  - <PARALLELISM>    (specialized info for parallel runs)
  - <CHARGE-DENSITY>
  - <TIMESTEPS>      (positions, velocities, nose' thermostats)
  - <BAND_STRUCTURE_INFO>    (dimensions and basic data about band structure)
  - <EIGENVALUES>    (eigenvalues and related data)
  - <EIGENVECTORS>   (eigenvectors and related data)

  
* Tag description

  <HEADER> 
     <FORMAT>    (name and version of the format)
     <CREATOR>   (name and version of the code generating the file)
  </HEADER>

  <CONTROL>
     <PP_CHECK_FLAG>    (whether the file can be used for post-processing)
     <LKPOINT_DIR>      (whether kpt-data are written in sub-directories)
     <Q_REAL_SPACE>     (whether augmentation terms are used in real space)
  </CONTROL>

  <STATUS>  (optional)
     <STEP>   (number $n of steps performed, i.e. we are at step $n)
     <TIME>   (total simulation time)
     <TITLE>  (a job descriptor)
     <ekin>   (kinetic energy)
     <eht>    (hartree energy)
     <esr>    (Ewald term, real-space contribution)
     <eself>  (self-interaction of the Gaussians)
     <epseu>  (pseudopotential energy, local)
     <enl>    (pseudopotential energy, nonlocal)
     <exc>    (exchange-correlation energy)
     <vave>   (average of the potential)
     <enthal> (enthalpy: E+PV)
  </STATUS>

  <CELL>
     <BRAVAIS_LATTICE>
     <LATTICE_PARAMETER>
     <CELL_DIMENSIONS>  (cell parameters)
     <DIRECT_LATTICE_VECTORS>
        <UNITS_FOR_DIRECT_LATTICE_VECTORS>
        <a1>
        <a2>
        <a3>
     <RECIPROCAL_LATTICE_VECTORS>
        <UNITS_FOR_RECIPROCAL_LATTICE_VECTORS>
        <b1>
        <b2>
        <b3>
  </CELL>

  <IONS>
     <NUMBER_OF_ATOMS>
     <NUMBER_OF_SPECIES>
     <UNITS_FOR_ATOMIC_MASSES>
     For each $n-th species $X:
        <SPECIE.$n>
           <ATOM_TYPE>
           <MASS>
           <PSEUDO>
        </SPECIE.$n>
     <PSEUDO_DIR>
     <UNITS_FOR_ATOMIC_POSITIONS>
     For each atom $n of species $X:
        <ATOM.$n SPECIES="$X">
  </IONS>

  <SYMMETRIES>
     <NUMBER_OF_SYMMETRIES>
     <INVERSION_SYMMETRY>
     <NUMBER_OF_ATOMS>
     <UNITS_FOR_SYMMETRIES>
     For each symmetry $n:
        <SYMM.$n>
           <INFO>
           <ROTATION>
           <FRACTIONAL_TRANSLATION>
           <EQUIVALENT_IONS>
        </SYMM.$n>
  </SYMMETRIES>

  <ELECTRIC_FIELD>  (optional)
     <HAS_ELECTRIC_FIELD> 
     <HAS_DIPOLE_CORRECTION>
     <FIELD_DIRECTION>
     <MAXIMUM_POSITION>
     <INVERSE_REGION>
     <FIELD_AMPLITUDE>
  </ELECTRIC_FIELD>  

  <PLANE_WAVES>
     <UNITS_FOR_CUTOFF>
     <WFC_CUTOFF>
     <RHO_CUTOFF>
     <MAX_NUMBER_OF_GK-VECTORS>
     <GAMMA_ONLY>
     <FFT_GRID>
     <GVECT_NUMBER>
     <SMOOTH_FFT_GRID>
     <SMOOTH_GVECT_NUMBER>
     <G-VECTORS_FILE>       link to file "gvectors.dat"
     <SMALLBOX_FFT_GRID>
  </PLANE_WAVES>

  <SPIN>
     <LSDA>
     <NON-COLINEAR_CALCULATION>
     <SPIN-ORBIT_CALCULATION>
     <SPIN-ORBIT_DOMAG>
  </SPIN>

  <EXCHANGE_CORRELATION>
     <DFT>
     <LDA_PLUS_U_CALCULATION>
     if LDA_PLUS_U_CALCULATION
        <NUMBER_OF_SPECIES>
        <HUBBARD_LMAX>
        <HUBBARD_L>
        <HUBBARD_U>
        <HUBBARD_ALPHA>
     endif
  </EXCHANGE_CORRELATION>

  if hybrid functional
      <EXACT_EXCHANGE>
        <x_gamma_extrapolation>
        <nqx1>
        <nqx2>
        <nqx3>
        <exxdiv_treatment>
        <yukawa>
        <ecutvcut>
        <exx_fraction>
        <screening_parameter>
      </EXACT_EXCHANGE>
  endif 

  <OCCUPATIONS>
     <SMEARING_METHOD>
     if gaussian smearing
        <SMEARING_TYPE>
        <SMEARING_PARAMETER>
     endif
     <TETRAHEDRON_METHOD>
     if use tetrahedra
        <NUMBER_OF_TETRAHEDRA>
        for each tetrahedron $t
           <TETRAHEDRON.$t>
     endif
     <FIXED_OCCUPATIONS>
     if using fixed occupations
        <INFO>
        <INPUT_OCC_UP>
        if lsda
           <INPUT_OCC_DOWN>
        endif
     endif
  </OCCUPATIONS>

  <BRILLOUIN_ZONE>
     <NUMBER_OF_K-POINTS>
     <UNITS_FOR_K-POINTS>
     <MONKHORST_PACK_GRID>
     <MONKHORST_PACK_OFFSET>
     For each k-point $n:
        <K-POINT.$n>
  </BRILLOUIN_ZONE>

  <PHONON> 
     <NUMBER_OF_MODES>
     <UNITS_FOR_Q-POINT>
     <Q-POINT>
  </PHONON>

  <PARALLELISM>
     <GRANULARITY_OF_K-POINTS_DISTRIBUTION>
  </PARALLELISM>

  <CHARGE-DENSITY>
      link to file "charge_density.rho"
  </CHARGE-DENSITY>

  <TIMESTEPS>  (optional)
     For each time step $n=0,M
       <STEP$n>
          <ACCUMULATORS>
          <IONS_POSITIONS>
             <stau>
             <svel>
             <taui>
             <cdmi>
             <force>
          <IONS_NOSE>
             <nhpcl>
             <nhpdim>
             <xnhp>
             <vnhp>
          <ekincm>
          <ELECTRONS_NOSE>
             <xnhe>
             <vnhe>
          <CELL_PARAMETERS>
             <ht>
             <htve>
             <gvel>
          <CELL_NOSE>
             <xnhh>
             <vnhh>
          </CELL_NOSE>
  </TIMESTEPS>

  <BAND_STRUCTURE_INFO>
     <NUMBER_OF_BANDS>
     <NUMBER_OF_K-POINTS>
     <NUMBER_OF_SPIN_COMPONENTS>
     <NON-COLINEAR_CALCULATION>
     <NUMBER_OF_ATOMIC_WFC>
     <NUMBER_OF_ELECTRONS>
     <UNITS_FOR_K-POINTS>
     <UNITS_FOR_ENERGIES>
     <FERMI_ENERGY>
  </BAND_STRUCTURE_INFO>

  <EIGENVALUES>
     For all kpoint $n:
         <K-POINT.$n>
             <K-POINT_COORDS>
             <WEIGHT>
             <DATAFILE>                  link to file "./K$n/eigenval.xml"
         </K-POINT.$n>
  </EIGENVALUES>

  <EIGENVECTORS>
     <MAX_NUMBER_OF_GK-VECTORS>
     For all kpoint $n:
         <K-POINT.$n>
             <NUMBER_OF_GK-VECTORS>
             <GK-VECTORS>                link to file "./K$n/gkvectors.dat"
             for all spin $s
                <WFC.$s>                 link to file "./K$n/evc.dat"
                <WFCM.$s>                link to file "./K$n/evcm.dat" (optional)
                                         containing wavefunctions at preceding step
         </K-POINT.$n>
  </EIGENVECTORS>

6.2 Restart files

7 Modifying/adding/extending QUANTUM ESPRESSO

7.1 Programming style (or lack of it)

Guidelines for developers:

7.2 Adding or modifying input variables

New input variables should be added to ''Modules/input_parameters.f90'', then copied to the code internal variables in the ''input.f90'' subroutine. The namelists and cards parsers are in : ''Modules/read_namelists.f90'' and ''Modules/read_cards.f90''. Files ''input_parameters.f90'', ''read_namelists.f90'', ''read_cards.f90'' are shared by all codes, while each code has its own version of ''input.f90'' used to copy input values into internal variables

EXAMPLE: suppose you need to add a new input variable called ''pippo'' to the namelist control, then:

  1. add pippo to the input_parameters.f90 file containing the namelist control
                  INTEGER :: pippo = 0
                  NAMELIST / control / ....., pippo
    
    Remember: always set an initial value!

  2. add pippo to the control_default subroutine (contained in module read_namelists.f90 )
                   subroutine control_default( prog )
                  ...
                  IF( prog == 'PW' ) pippo = 10
                  ...
                  end subroutine
    
    This routine sets the default value for pippo (can be different in different codes)

  3. add pippo to the control_bcast subroutine (contained in module read_namelists.f90 )
                    subroutine control_bcast( )
                    ...
                    call mp_bcast( pippo )
                    ...
                    end subroutine
    


8 Using SVN

The package is available read-only using anonymous access to the Subversion (SVN) repository. Developers can have read-write access when needed. Note that the latest (development) version may not work properly, and sometimes not even compile properly. Use at your own risk.

Subversion, also known as SVN, is a software that allows many developers to work and maintain a single copy of a software in a central location (repository). It is installed by default on many Unix machines, or otherwise it can be very easily installed. For the end user, SVN is rather similar to CVS: if no advanced features are used, the basic commands are the same. More information on SVN can be found here: http://subversion.apache.org/.

Follow the instructions in the SCM page in qe-forge.org for the QUANTUM ESPRESSO project: http://qe-forge.org/scm/?group_id=10, to check out (i.e. download) the SVN repository in either read-write or anonymous mode. The distribution will appear in directory trunk/espresso/. Branches (i.e. sub-versions) will appear as separate directories.

8.1 SVN operations

To update the code to the current version:

  svn update
in the directory containing the distribution. To see the difference between the current version and your modified copy:
  svn diff
To save your modified version into the repository: (read-write access only):
  svn commit
If you also want to add a new file, before commiting give command
  svn add


8.2 Removing conflicts

Look into the conflicting section: in most cases conflicts are trivial (format changes, white spaces) or easily solved (the part of the code you were modifying has been moved to another place, for instance). Sometimes, somebody else has done changes that are incompatible with yours during the same period. Use the web-svn interface:
   http://qe-forge.org/scm/browser.php?group\_id=10
You can select the repository at a given date or with a given ``tag'': this may be useful if if you suspect that the incompatibile change happened after that date.

9 bibliography

Fortran books:

On-line tutorials: (info courtesy of Goranka Bilalbegovic)

About this document ...

Image quantum_espresso Image democritos
Developer's Manual for QUANTUM ESPRESSO(v. 4.3.1)

This document was generated using the LaTeX2HTML translator Version 2008 (1.71)

Copyright © 1993, 1994, 1995, 1996, Nikos Drakos, Computer Based Learning Unit, University of Leeds.
Copyright © 1997, 1998, 1999, Ross Moore, Mathematics Department, Macquarie University, Sydney.

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The translation was initiated by Paolo Giannozzi on 2011-07-17



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Paolo Giannozzi 2011-07-17