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Since the beginning of the century, Wien2K has proven to be a very powerful player in computational condensed matter and materials physics.

Wien2K is an all-electron periodic DFT code based on the Augmented Planewave + Local Orbital [APW+lo] method, and also widely known as Full-Potential - Linearized Augmented Planewave [FP-LAPW+lo] method, or simply LAPW. It is known or said to be one of the most accurate methods for modeling solids. Wien2K is very nice, but it is not free.

Do you know of any open-source & community LAPW codes alternative to Wien2K?

What has been your experience with them?

I am particularly interested in codes that invite developers.

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    $\begingroup$ According to this, the free ones that have APW listed under "basis", are elk, EXCITING, HiLAPW (seems defunct), and FLEUR. Someone with more experience with these codes (or a developer of them) can answer. I could give an answer perhaps for FLEUR to give an example of a good answer format. $\endgroup$ Jul 16 '20 at 12:13
  • $\begingroup$ @NikeDattani I think you should convert your comment to an answer. $\endgroup$ Jul 17 '20 at 10:29
  • $\begingroup$ @SusiLehtola I have no experience in the field of APW (don't even know what it is!) and haven't used any of these codes, but I found based on some searching, that it seems these are the 4 open-source codes that use APW. FLEUR seemed the easiest to explain so I'll try to write an answer on FLEUR when I get a chance. Hopefully some people will be able to answer about the other 3 too :) $\endgroup$ Jul 17 '20 at 14:17
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    $\begingroup$ In the end I decided to explain Elk, and someone else can explain FLEUR. EXCITING is related to Elk (but has a completely different website, so it might still be useful for someone to explain it). HiLAPW seems to be defunct, but someone might still wish to explain it. $\endgroup$ Jul 17 '20 at 21:57
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    $\begingroup$ I briefly though of NWChem - apparently not... I found this though: dft.sandia.gov/Quest/DFT_codes.html Enjoy the link, and hopefully someone with experience can turn it into a proper answer. $\endgroup$
    – DetlevCM
    Jul 18 '20 at 7:57
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Elk

  • Free, and can be redistributed or modified under the terms of GPU General Public Licesence.
  • Well explained on this webpage.
  • Well documented in this PDF file.
  • Interacts with the following codes:
    • Wannier90
    • Phonopy
    • NOMAD
    • Libxc
    • ASE
    • DGrid
    • Elk optics Analyzer
    • PyProcar
  • Advertised in a few places as being focused strongly on being simple and easy to develop.
  • Written in FORTRAN 2003 and an advertised strength is that it's all written in one language.

Finally, you said that you were particularly interested in codes that invite developers, and this exactly the case with Elk "Groups and individuals are actively encouraged to develop and release their own specialised versions of the Elk code under the GPL". The Wannier90 interface mentioned above, was developed by people in Sweden and Russia, who were not part of the original Elk team.

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    $\begingroup$ Awesome job, as always Nike! $\endgroup$ Jul 17 '20 at 21:58
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Elk / EXCITING

Like @Nike Dattani suggested, Elk is an open-source well-documented FP-LAPW DFT package. Also, LAPW stands for Linearly-Augmented Plane Wave. Singh's book is an excellent introduction for this topic. (Disclaimer: I'm currently developing an extension to Elk / EXCITING to compute response functions and estimate Hubbard model parameters using the constrained RPA method, here in our research group at U. of Tennessee. Coincidentally the "working" name of the package is Exciting-Plus, but it's still being optimized so not ready for public use yet.)

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Questaal

  • Questaal is a suite of electronic structure programs. The codes can be used to model arbitrary materials, but they are mostly designed to answer condensed-matter theory questions about solid-state (periodic) structures. The majority of the codes use an all-electron implementation of density-functional theory. This includes several forms (Hamiltonian and Green’s function) that serve different purposes. There is an all-electron implementation of GW theory, used most particularly in a quasiparticle self-consistent form (QSGW). Tight-binding based on user-supplied empirical Hamiltonians is also supported. Recent development work includes Dynamic Mean Field Theory (DMFT-QSGW), the Bethe Salpeter Equation (BSE), and direct (Green Function) solution of the Dirac equation.

  • Website: https://www.questaal.org/

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FLEUR

Disclaimer: I'm a developer of the Fleur code.

Fleur is a Fortran-based open source (MIT license) FLAPW(+LO) code under rapid development. A detailed user guide for the code is available on it's website and there also is a user forum. Fleur connects to numerous other software packages and frameworks. Among these are Spex (A GW code), Wannier90, AiiDA (for workflow automatization and provenance tracking), and LibXC.

Work on Fleur is mainly performed by the development group in Jülich. External development is appreciated, please register on the gitlab page to be able to contribute. I suggest that people interested in contributing to the code or basing their developments on the code get in contact with the group to find out how this is best done.

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CP2K

This program can do all-electron calculations using the GAPW method.

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    $\begingroup$ I gave you +1, but please take note of my edit which tries to format the answer a bit better :) $\endgroup$ Dec 2 '20 at 21:31

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