v0.6.20

DFTK v0.6.20

Diff since v0.6.19

Merged pull requests:

• Virial interface for AtomsCalculator (#959) (@CedricTravelletti)
• Calculator State (#961) (@CedricTravelletti)
• Add a preference option for DFTK threading (#972) (@antoine-levitt)
• Ignore optim_res when saving scfres (#973) (@antoine-levitt)
• Improve performance of stress calculations (#978) (@mfherbst)
• Use the Simpson rule for integration of local part of PSPs (#982) (@abussy)
• fix typo (#983) (@chillenb)
• Update chat url to zulip (#984) (@mfherbst)
• Updating TestItemRunner (#989) (@epolack)
• Update Hartree potential notation in introductory docs (#990) (@niklasschmitz)

Closed issues:

• Stresses need an unreasonable amount of memory and runtime (#893)
• Incompatible with TestItemRunner 1.0 (#988)