Multireference wave function methods are important tools in the quantum chemist's arsenal, for the description of static correlation in systems with stretched bonds or other types of (near-) degeneracies, as well as open-shell systems including radicals and excited states. However, the exponential scaling of computational cost with respect to active space size, for methods such as the complete active-space self-consistent field (CASSCF) theory, limits the size and scope of problems that can be addressed in this way. To reduce the cost of multireference approaches, alternative ansätze have been developed, notably spin-flip (SF) methods. Amongst the SF family of approaches, one of the most important variants is the restricted active space (RAS-)SF method. Configuration interaction (CI) wave functions within the RAS family include all possible configurations within an active space, and (at a minimum) single excitations into and out of the active space. As such, RAS-SF provides a low-cost, balanced treatment of ground and excited states with multi-radical character. Unlike CASSCF, the RAS-SF technique does not require orbital optimization, which significantly reduces both complexity and cost. A recently-developed variant of RAS-SF allows analysis of charge-transfer (CT) states, which were previously inaccessible to the theory. The new method can compute not just CT states but also electronic couplings, * herbert@chemistry.ohio-state.edu using a diabatic framework that may facilitate more indepth understanding of photophysical processes such as artificial or biological light-harvesting. The position of CT states in the excitation manifold is often sensitive to polarization effects, even in low-dielectric environments such as organic photovoltaic materials. Therefore some treatment of the surrounding medium is likely necessary in order to make contact with experiments.