Efficient Calculation of the Dispersion Energy for Multireference Systems with Cholesky Decomposition: Application to Excited-State Interactions

Accurate and efficient prediction of dispersion interactionsinexcited-state complexes poses a challenge due to the complex natureof electron correlation effects that need to be simultaneously considered.We propose an algorithm for computing the dispersion energy in nondegenerateground- or excited-state complexes with arbitrary spin. The algorithmscales with the fifth power of the system size due to employing Choleskydecomposition of Coulomb integrals and a recently developed recursiveformula for density response functions of the monomers. As a numericalillustration, we apply the new algorithm in the framework of multiconfigurationalsymmetry adapted perturbation theory, SAPT(MC), to study interactionsin dimers with localized excitons. The SAPT(MC) analysis reveals thatthe dispersion energy may be the main force stabilizing excited-statedimers.