The Frenkel exciton model is a useful tool for coarse-graining electronic structures of multichromophoric systems. In particular, ab initio exciton model has proven powerful in theoretical simulations of large and complicated systems like light-harvesting complexes. However, conventional implementations take into account only excitons that are localized on chromophore monomers. To make the model more general, we first expanded the ab initio exciton model by including the charge-transfer excited states, and demonstrated that the model is robust and predicts reliable charge-transfer excitation energies and asymptotic behavior. We then further expanded the ab initio exciton model by incorporating the singlet-coupled triplet pair, the key excited states in singlet fission. Comparison with multiconfigurational methods confirms that our exciton model predicts consistent energies and couplings and captures the correct physics. The development of the excitation energies, couplings and analytical derivatives for the ab initio exciton model allows nonadiabatic simulations of excited state dynamics by means of ab initio multiple spawning technique. We show the possibility of carrying out molecular dynamics simulations on adiabatic energy surfaces as well as nonadiabatic dynamics simulations to properly model population transfer between electronic states.