Integrate tblite library for evaluating xTB Hamiltonians

[awvwgk]

• [x] enable optional build with tblite
  • [x] support as feature in meson (default: auto-detect)
  • [x] support as option CMake (default: off?)
• [x] provide calculator implementation
  • [x] basic single point calculator
  • [x] allow selection of method or parameter file
  • ~~allow creation of solvation models~~ (separate PR)
  • ~~provide info printout from parametrization~~ (separate PR)
• [ ] regression tests
• [x] documentation about new option

Closes #514

[awvwgk]

This is mostly complete, in case anyone is interested in helping to get it merged let me know.

[awvwgk]

Ready for review.

[MtoLStoN]

I cannot compile a static version of this anymore with the latest intel compiler (using -static -OpenMP linking flags). However, some trial and error let me narrow this down to the ifcore library, which is probably used by one of the subprojects (json_fortran?). Adding an explicit -lifcoremt to the linker flags fixes this for me.

A way to fix this via the meson build system would be to add an ifcoremt library dependency to tblite.

lib_deps += fc.find_library('ifcoremt')

somewhere here https://github.com/tblite/tblite/blob/fa115545f7a6ba8e3f0e62df5cdace8781f4d309/config/meson.build#L143-L145

But this probably needs to be customized for the various compilers we use.

[awvwgk]

Yes, that is due to libraries without direct OpenMP dependency in the tree, but will only pop up for static linking with Intel. For dist I recommend to use

Linux

meson setup _build \
    -Dprefix=/ \
    -Dlibdir=lib \
    -Dbuildtype=release \
    -Dfortran_link_args="-lifcoremt -static" \
    -Ddefault_library=static \
    -Dlapack=mkl
meson compile -C _build
meson install -C _build --destdir $PWD/xtb-dist

Windows (powershell)

meson setup _build `
    -Dfortran_args="/fpp" `
    -Ddefault_library=static `
    -Db_vscrt=mt `
    -Dbuildtype=release `
    -lapack=custom `
    -Dfortran_link_args="mkl_intel_lp64.lib mkl_intel_thread.lib mkl_core.lib libiomp5md.lib ifcoremt.lib /STACK:16777216"
meson compile -C _build
meson install -C _build --destdir $pwd\xtb-dist
cp $env:MKLROOT\..\..\compiler\latest\windows\redist\intel64_win\compiler\libiomp5md.dll xtb-dist\bin

Might work to just drop-in -Dfortran_args=-qopenmp / -Dfortran_args=/qopenmp instead of messing with the link arguments.

[MtoLStoN]

Agree. As stated, adding an explicit -lifcoremt linker flag works for me for static linking. However, the dynamic build needs an additional "-qopenmp" linker flag to compile, which is nothing terrible, but we should probably include that in the README to prevent future questions.

Otherwise, this looks good to me.

[MtoLStoN]

Thanks for sharing.