Electron transfer processes are ubiquitous in chemistry and of great importance in many systems of biological and commercial interest. The ab-initio description of these processes remains a challenge in theoretical chemistry, partly due to the high scaling of many post-Hartree--Fock computational methods. This poses a problem for systems of interest that are not easily investigated experimentally. We show that readily available Hartree--Fock solutions can be used as a quasidiabatic basis to understand electron transfer reactions in a Marcus framework. Non-orthogonal configuration interaction calculations can be used to quantify interactions between the resulting electronic states, and to investigate the adiabatic electron transfer process. When applied to a titanium-alizarin complex used as a model of a Gr"atzel-type solar cell, this approach yields a correct description of the electron transfer and provides information about the electronic states involved in the process.