VASP POSCAR format

[seatonullberg]

I was surprised to see VASP's structure file format not listed in the supported formats. The format is notoriously underspecified but the official reference can be found here. I would be happy to contribute if someone is not already working on it.

[Luthaf]

We don't support POSCAR yet, but it would make for a great addition! Nobody is working on it at the moment AFAIK.

It seems to be a free-form line oriented text format, so it would be a child class of TextFormat in chemfiles, doing the reading/writing through a TextFile, and you might be interested in the scan function to extract whitespace separated values. Let me know if you have any more questions!

[seatonullberg]

Thanks to all the contributors for making such thorough documentation! One question I do have, however, is how to add data files to test the new format implementation?

[Luthaf]

That's something we still have to document. The files live in https://github.com/chemfiles/tests-data, so you can make a PR there. Then, they are downloaded in

chemfiles/tests/CMakeLists.txt

Lines 1 to 11 in 76e7799

	# Update this value if you need to update the data file set
	set(TESTS_DATA_GIT "268c5ec327b4c704597f78f9effa0bb1efb3c299")
	if(NOT EXISTS "${CMAKE_CURRENT_BINARY_DIR}/data/${TESTS_DATA_GIT}")
	message(STATUS "Downloading test data files")
	file(DOWNLOAD
	"https://github.com/chemfiles/tests-data/archive/${TESTS_DATA_GIT}.tar.gz"
	"${CMAKE_CURRENT_BINARY_DIR}/${TESTS_DATA_GIT}.tar.gz"
	SHOW_PROGRESS
	EXPECTED_HASH SHA1=fdfd48b32e97b9abf7da4ad8d29c0cde87271a48
	)

So you can update the git SHA1 & hash to update the downloaded files. They are finally accessible in tests at the data/xxx/zzz.xyz path.

The idea of having a separate repository for data files allow to decrease the size of the main repository, which is nice for users that might not want to run tests.