quantum-espresso/TODO

TODO LIST - September 2010


0) Suspected bugs/problems:
  0.1  electric field in hexagonal lattice
  0.2  "image" parallelization in CP
  0.3  projwfc in CP doesn't work for spin polarized case
  0.4  FFT grid dimensions not the same in PW and in CP for same data
       (requires merge of all FFT-related variables between CP and PW)
  0.5  Small energy differences between PW and CP - maybe PP-related, 
       but might also be a problem of Ewald calculation in CP ("raggio"?)
  0.6  Numerical instabilities with BLYP and TPSS

1) Organization

1.1 www.quantum-espresso.org:
  1.1.0 Better download page that allows selection of packages
        (see 1.3.0)
  1.1.1 update home page picture and sample applications
  1.1.2 pseudopotential upload facility:
        there is a problem with link to *.info files
1.2 Wiki:
  1.2.1 what is left now: list of papers, bibliography, misc stuff.
        The list of papers should be replaced by a query to some
        database for cited papers.
1.3 CVS/packaging:
  1.3.0 Rethink a directory structure that better reflects the structure
        of QE as packages (see 1.1.0, 2.0). Lots of files to be moved
        around: a good reason to move to subversion?
  1.3.1 no pseudopotentials in CVS any longer. Examples should download
        needed PPs from the web site (with a wget)
  1.3.2 run source-normalizer script dev-tools/src-normal
  1.3.3 The partition of code among directories should be reconsidered.
        There are circular dependencies that make the installation mechanism
        a mess, cause trouble with linkers unable to resolve cross-references:
        files in flib/ use modules in Modules/, while files in Modules in 
        turn call files in flib/; Modules/mm_dispersions.f90 calls PW/rgen.f90;
        neb modules in Modules/ calling compute_scf in PW and CP...
  1.3.4 Everything that is not in the " QE core" or that is used only for 
        special purposes (e.g.: EE/+Multigrid/) should be extracted and 
        moved into external libs or plugins or whatever is appropriate
1.4 mailing lists:
  1.4.1 add somewhere instructions on netiquette and how to post 
        Send monthly reminder?
  1.4.2 move to qe-forge, changing names
1.5 Interoperability:
  1.5.1 we should maintain somewhere (user guide? wiki? web page?)
        a list of external "QE-interoperable codes", that either
        provide input data for QE or read output/data files from QE
1.6 qe-forge:
  1.6.1 there should be somewhere a short introduction to qe-forge and
        its usage

2) Documentation

2.0 We should decide a strategy on where to put the documentation.
    Now it is in Doc/ for everything, except for atomic/ and GWW/.
    We should decide which packages should have the documentation
    in other places. The same applies to examples. See 1.3.0
2.1 Better (and shorter) FAQ list. Notably missing:
    - hardware for QE
    - segmentation fault (present but not visible enough)
2.2 QE-Tutorial: should be moved to the cvs or svn of qe-forge.
2.3 Documentation on how to generate PP for GIPAW calculation is missing
2.4 Documentation and examples for EE/ stuff are absent

3) Pseudopotentials 

3.0 Set up standard tests for all PPs
3.1 Add Coulomb PPs to PP library - requires extending the name
    convention to cover this case and updating the scripts that
    generate the PP table
3.2 Implement Goedecker PPs
3.3 Implement OEP PPs
3.4 Standard recipe for generating reasonable PPs:
    - Set of prescriptions for generation
    - Criteria for portability
    - Update PP table with PPs that follow the recipe
3.5 Extend documentation in pseudo-gen.tex to the case of multiple
    projectors and to USPP (eventually to PAW) - add *.pdf
3.6 Add default cutoff values as well as radii of augmented charge
    in pseudopotential files (they are present in recent PP only)
3.7 The intermediate hard NCPP is useless for PAW and should not be 
    done when generating a PAW set
3.8 Finish merge of Meta-GGA (TPSS) code into atomic code
3.9 Pseudopotential files are read in parallel by all processors.
    They should be read by one processor, broadcast to all others.
    Also: when restarting, the copy of the PP in the restart file
    should be read.

4) Development

4.0  Major highly desirable restructuring:
  4.0.1  Add the possibility to run NEB/PH in a dynamical way, with a
         home-made scheduler that executes tasks as soon as resources are
         free; might be used for image parallelization as well.
  4.0.2 Better-structured relaxation and molecular dynamics (including the
        variable-cell case), with more extenisive integration of PW and CP
  4.0.3 Image parallelization on k-points of EXX should be replaced by 
        pool parallelization.

4.1  New developments to be added (sooner or later):
  4.1.1 Moka structure builder + new xml input/output (RS)
  4.1.2 XMCD in XSpectra
  4.1.3 vdW with nonlocal xc functional
  4.1.4 new GWW
  4.1.5 EPW (electron-phonon with Wannier stuff)
  4.1.6 G-space symmetrization also for phonons. In the meantime:
        rimove check on nonsymmorphic symmetries in pw.x, leave it only
        in the phonon code
  4.1.7 bio-oriented stuff :
        - MS2 plugin for QM-MM
        - Solvent Models
        - PCM
  4.1.8 Wannier-based exact-exchange in CP (available)
  4.1.9 Wannier-based exact-exchange in PW (to be done)

4.2 Small new developments, desirable or to be added:
  4.2.0 fractional charge (nelec/nelup/neldw)? is it working?
  4.2.1 configure issues:
        - ifort+acml
        - ifort+mkl+scalapack troubles
        - add search for -lfftw3xf_intel 
        - remove obsolete stuff: next is macppc
  4.2.2 constraints should be implemented in all cases;
        a check should be added if constraints break the symmetry
  4.2.3 inversion symmetry should allow real hamiltonian and wavefunctions
  4.2.4 nscf calculations are slow. There must be a way to make a better
        usage of the available information from the scf calculation:
        wavefunctions are just discarded. Same for phonon calculation: 
        it shouldn't be needed to recalculate everything almost from
        scratch at each different q-point
  4.2.5 Fermi-Dirac: pass T instead of "broadening", make it possible
        to use it on top of smearing for free-energy calculations
  4.2.6 add traceback in error (error_handler module)
  4.2.7 matdyn should write frequencies in a format that is suitable
        for direct plotting by gnuplot/xmgrace - see also Eyvaz' script
        for phonon plotting. Also about phonons:
        - C(R) should be calculated at the end of a dispersion run
        - projected phonon DOS with tetrahedra
        - adapt plotband.x to phonon case; in general, simplify phonon plotting
        - QHA calculations inside matdyn? see fqha.f90
  4.2.8 Interface to RESP calculation - requires adding radii to xml file
  4.2.9 elf for USPP/PAW ; delocalization indices
  4.1.10 Collection of tools and utilities for data analysis 
         (things like g(r) from MD simulations). Also: for ev.x,
         write output file with E(V) for direct plotting of EOS
  4.2.11 Gamma: same input as for PH
  4.2.12 Cleanup of the 'prefix.EXIT' stuff. Stop with signals?
         Also: stop with 'prefix.EXIT' and restart in D3 and Gamma (KK)
  4.2.13 Various defaults for CP (proposed from Princeton):
       - emass(emass=300), dt (dt=7), for preconditioning cutoff (3)
       - automatic box grid for USPP from radii of augmented charge
      - Electronic minimization: damp as default, sd discouraged
         introduce an automatic default schedule, something as:
         1st step sd followed by 5 steps with with damp= 0.8,
                     followed by 5 steps with damp=0.5,
                     followed by 10 steps with damp=0.3,
                     followed by 10 steps with damp=0.2,
                     followed by as many steps as necessary
                     to achieve the required convergence with damp=0.1
        A max number of steps should be included to ensure program termination.
        The other option allowed should be conjugate gradients:
       see NM - it could one day become the default
      -  Ionic minimization: again SD should be discouraged
         A default scheme for simultaneous damped dynamics should be given
         (to be tested) for example: zero damp on ions and start with damp=0.5
         on electrons to become then 0.1 or perhaps the values should be set
         given the forces on the ions
         When moving ions and electrons simultaneously an important parameter
         is the ratio between electron and ion masses - For minimization it 
         is better to set up all the ion masses equal - A default value for
         the ion masses (considering the defaults for emass and dt) is perhaps
         10 AMU (we should do some test to see if 20 AMU is s a safer value)
      - Default values for randomization should be given
        amprp=0.1 is a decent value - amprp=0.01 is too small
      - Car-Parrinello dynamics: the proper masses for the ions, an optimal
        value for emass and dt should be set up by the code, based on the 
        smaller atomic mass and the default value used in the minimization
        e.g. Amass_default=10 AMU. If the minimum physical AMASS is 20 then
        dt=sqrt(2) dt_default and emass should be increased so to keep
        emass^2/dt constant
      - defaults for the Nose thermostat
  4.2.14 -DEXX should be removed, or at least it should be confined to just
         some specialized parts of the code.

4.3 Performance enhancements/Parallelization:
  4.3.1 make hpsi/spsi/CG  faster
        - remove complex factor i**l from beta fct and q(r)
        - shift structure factor from beta to psi when computing becp 
          (reduce memory)
        - use real BLAS routine instead of COMPLEX one in hpsi/spsi 
          (at least 2 times faster).
        - use only half of the G's when computing real integrals
          (2 times faster)
        - seek for CG and DIIS algoritms that only use (H-eS)|psi>
          and not the two vector separately ... compute it in one single
          call. In this way S|psi> is inexpensive
  4.3.2 Try the new "Density-Matrix-Based" diagonalization algorithm
  4.3.3 image parallelization of the phonon code: irreps and q-vectors
        should be distributed across processors/grid computers.
        Could be done in the same way as for NEB?
  4.3.4 PH: use charge mixing instead of potential mixing
  4.3.5 D3: verify status of parallelization, clean it up if needed

4.4 Cleanup
  4.4.1 Increase modularization by 
        - collecting variables and routines acting on those variables
          into modules
        - classifying modules in a hierarchical way
        - avoiding as much as possible that modules depend on many
          other modules
  4.4.2 Avoid monster routines that do too many things at the same time
        depending on the value of too many variables. An example:
        read_file, readpp
  4.4.3 There is some confusion in the various initialization steps:
         - default values at startup
         - reading of the input data and copy into internal variables
         - reading from data file
         - initialization of general variables (that presumably will
           be written to or read from file)
         - initialization of variables used in a specific calculation
          (that may not be written to or read from the data file)
        All these steps are intermixed and/or replicated and it is 
        never clear what is initialized where. Same for variable
        allocation: see recent GIPAW workaround for an example of
        allocation confusion (qnorm, cell_factor in allocate_nlpot)
  4.4.4 More PW/CP merge:
        - lda+U modules
        - "cell_base_init" from CP to PW
        - "cellmd" module of PW and "cell_base" of CP
        - PW "real-space" approach / CP "small boxes" 
        - there should be a single function or routine for periodic boundary 
          conditions (i.e. bringing all atoms inside the unit cell)
        - spherical harmonics and integration routines
        - merge of atomic positions! currently CP uses a complex logic
          that is very hard to follow
  4.4.6 adding/removing/modifying input variables is too complex
        Why are some checks on input variables performed in read_namelist,
        while others apparently similar are in */input.f90?
  4.4.7 Units: all units should be clearly documented and printed 
        on output (and also it should be clearly stated what the
        printed quantites are)
  4.4.8 There should be a function calculating dj_l/dx;
        j_l with l=-1 should not be needed
  4.4.9 too many confusing error messages are still around
  4.4.10 Output should be more informative and less confused, better
         structured, and ready for automatic reading (.e.g by xcrysden)
  4.4.11 any possibility to merge the various solve_* in PH ?
  4.4.12 Replace "use pwcom" with more "use" statements
  4.4.13 Move all plots requiring Fourier (or real-space) interpolation
         into pawplot.x, leaving in pp.x only gaussian cube and 3d xsf
         files. Plots of sums and differences should be performed using
         data files ready for plotting (gnuplot, xsf, cube; may require
         some tools). pp.x should be simplified a lot and intermediate 
         format should disappear. Also: there is no reason to have dos.x
         together with projwfc.x
  4.4.14 All allocated variables should be deallocated at the end:
         it makes easier to find memory leaks. Currently most variables
         are deallocated, but a few (mostly in ffts and in pseudopotential
         reading) aren't
  4.4.15 __PARA and __MPI are redundant: one of them is sufficient
  4.4.16 add_efield must be rewritten from scratch: it is a mess beyond control
  4.4.17 Replace generic &inputpp namelist with code-specific namelist in
         postprocessing (Tone). Maybe at least some postprocessing codes 
         could be used with command-line options instead of fortran input?
  4.4.18 What about transforming 'bands'/'nscf' into a postprocessing
         code?

4.5 Trouble-makers. inconsistencies, etc
  4.5.1 Negative Charge problems (see qe-forge, H on graphene)
  4.5.3 G-vector shells, especially in the variable-cell case, and the 
        various tricks to reduce cpu by not re-calculating things that 
        depend on |G| only (see e.g. qvan2). Maybe we should move to 
        interpolation of all quantities and get rid of shells and tricks
  4.5.4 PP: complete postprocessing in Gamma case (only average missing),
        and with CP data (in the latter case: when the data file does
        not contain the charge/potential, issue an error message saying
        what is missing and why instead of just crashing in iotk)
  4.5.5 CP: add error check if dt^2/emass too large does not allow ortho
        to converge or cause energy to increase as time step evolve
  4.5.6 epsilon.x should be extended at least to have the nonlocal
        contribution included; there should be a pointer in the
        documentation explaining how to make a better calculation.
  4.5.7 There should be a check on the FFT grid preventing a bad 
        choice of Nr1,Nr2,Nr3 (e.g. different Nr for axis of the
        same length or even worse related by symmetry): this is a
        frequent source of trouble with electron-phonon calculations
  4.5.8 Still a few quirks with the atomic coordinate parser, if 
        DOS characters or tabulators are present (Lorenzo)
  4.5.9 Spin-polarized cases: clumsy, error-prone input (e.g.:
        occupations='fixed' vs 'from_input', input card)
 4.5.10 k-points in crystal IBZ should be correctly calculated also
        if input k-points are not in the IBZ of the lattice. Is is
        sufficient to use brute forces instead of group theory:
        expand to full BZ, remove symmetry-equivalent k 

5) Files and I/O

 5.1 The "buffer" trick to keep wfc in memory wasn't such a great idea 
     after all: a better approach would be to have a k-point index
 5.2 Scratch files are a big mess. It should be possible to open files
     in places other than tmp_dir without resorting to obscure coding.
     This is especially serious for PH, D3 etc
 5.3 There should be a clearer distinction, both in the code and
     in the input data, between directories to be read (and left
     unchanged), directories to be (over-)written, temporary files
     or directories
 5.4 Many inconsistencies between PW and CP in the xml file format
     (and inconsistencies with the documentation). Also: CP should
     behave like PW and create a directory if not existent
 5.5 Use qexml for xml file processing so that a single, easily
     exportable routine, is used everywhere. Requires some though
     on how to deal with parallelism without filling qexml with
     parallel stuff. This is also an opportunity to update the
     file format (and the documentation) with 1) removal of obsolete
     variables, 2) addition of variables that should be present,
     3) possibility to reduce the number of files and directories
     (hardcoded limit, more kpoints per directory, would replace
     and extend lkpoint_dir)
 5.6 There should be a lock mechanism that prevents people from
     overwriting files of running processes. Should be done with
     care, or else every time a code crashes will make the following
     one crash as well! 
 5.7 Add rotation of restart files, similar to what is done in CPMD:
    "The number of distinct RESTART files generated during CPMD runs
     is read from the next line. The restart files are written in turn.
     Default is 1. If you specify e.g. 3, then the files RESTART.1,
     RESTART.2, RESTART.3 are used in rotation."