where < Ξ 𝐴𝐴 𝐾𝐾𝑆𝑆 �𝐻𝐻 � �Ξ 𝐵𝐵 𝐾𝐾𝑆𝑆 > is obtained using the two BLKS determinant wave functions, The MS-EDA method has been implemented in the Qbics program in our laboratories, and a separate BLW-ED program 2 interfaced with the GAMESS-US package. The method and energy terms are illustrated by two excimer complexes: the asymmetric excimer complex of two acetone molecules (Figure ), and the pentacene dimer in three different geometry arrangements, including the optimized 𝑆𝑆 1 excimer, the stacked configuration of two pentacene monomers separated by 3.3 Å, each in the ground state geometry, and the fishbone configuration in the crystal used in an application to singlet fission (Figure ). MSDFT-NOSI and TDDFT calculations were carried out using the Minnesota M06-2X density functional along with the cc-pVDZ basis set for the pentacene excimer and cc-pVTZ for the acetone dimer. Geometries were optimized using Gaussian16. Throughout this Letter, we use electron volts (eV) as the energy unit to relate with electronic spectroscopy.