Accurate quantum chemical methods for the prediction of spin-state energy gaps for strongly
correlated systems are computationally expensive and scale poorly with the size of the system. This makes
calculations for many experimentally interesting molecules impractical even with abundant computational
resources. In previous work, we have shown that the localized active space (LAS) self-consistent field
(SCF) method is an efficient way to obtain multi-configuration SCF wave functions of comparable quality
to the corresponding complete active space (CAS) ones. To obtain quantitative results, a post-SCF method
is needed to estimate the complete correlation energy. One such method is multiconfiguration pair-density
functional theory (PDFT), which calculates the energy based on the density and on-top pair density obtained
from a multiconfiguration wave function. In this work we introduce localized-active-space pair-density
functional theory, which uses a LAS wave function for subsequent PDFT calculations. The method is tested
for computing spin-state energy gaps in conjugated organic molecules and bimetallic compounds and is
shown to give results within 0.05 eV of the corresponding CAS-PDFT results at a significantly lower cost.
A pair density functional theory utilizing the correlated wave function
