  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.
