Merge branch 'dev/prop' into 'master'

Implementation of the density matrix

See merge request !5
4 jobs for master in 15 minutes and 11 seconds (queued for 9 seconds)
latest
Status Name Job ID Coverage
  Build
passed gnu (debug) #58735
ubuntu

00:03:00

passed gnu-hybrid (debug) #58736
ubuntu

00:04:49

passed ifort (debug) #58733
ubuntu

00:04:05

passed ifort-omp (debug) #58734
ubuntu

00:03:15