  The computation of excited electronic states with commonly employed
(approximate) methods is challenging, typically yielding states of lower
quality than the corresponding ground state for a higher computational cost. In
this work, we present a mean field method that extends the previously proposed
eXcited Constrained DFT (XCDFT) from single Slater determinants to ensemble
1-RDMs for computing low-lying excited states. The method still retains an
associated computational complexity comparable to a semilocal DFT calculation
while at the same time is capable of approaching states with multireference
character. We benchmark the quality of this method on well-established test
sets, finding good descriptions of the electronic structure of multireference
states and maintaining an overall accuracy for the predicted excitation
energies comparable to semilocal TDDFT.
