We present a quantum embedding method for ground and
excited states
of extended systems that uses multiconfiguration pair-density functional
theory (MC-PDFT) with densities provided by periodic density matrix
embedding theory (pDMET). We compute local excitations in oxygen mono-
and divacancies on a magnesium oxide (100) surface and find absolute
deviations within 0.05 eV between pDMET using the MC-PDFT, denoted
as pDME-PDFT, and the more expensive, nonembedded MC-PDFT approach.
We further use pDME-PDFT to calculate local excitations in larger
supercells for the monovacancy defect, for which the use of nonembedded
MC-PDFT is prohibitively costly.