The correct syntax here would be !greenx, but we currently only use it for leak sanitizer and I don't think we should start using it for features.

I think, an input file should either produce the same result regardless of the presents of a library or fail if the required library is missing.

So, if GreenX produces significantly different results then it's essentially a different method and therefore merits an input keyword to enable/disable it.

Hi Ole, I see your point and I was thinking about this, too. For a few cases, greenX and the internal minimax have slightly different grids. Because of numerical instabilities, this affects the results, but only for small grids. For those, I relaxed either the tolerance a little or I used a larger, numerically more stable grids. I can fix the "regtest-rpa-sigma" tests in a similar manner; I have to admit I was a little lazy here. The other case "QS/regtest-gw-kpoints" I would leave because the tests are already relatively long and a larger grids makes them even longer...

Sounds like well balanced plan 👍

I'd suggest we use !greenx only for the transition period and once we have GreenX in the toolchain we change the reference values and switch to greenx (without the !).