excitons

Reining, L., Pulci, O., Palummo, M., & Onida, G. (2000). First-principles calculations of electronic excitations in clusters. Int. J. Of Quantum Chemistry, 77, 951-960.

Koskelo, J., Fugallo, G., Hakala, M., Gatti, M., Sottile, F., & Cudazzo, P. (2017). Excitons in van der Waals materials: From monolayer to bulk hexagonal boron nitride. Phys. Rev. B, 95, 035125. https://doi.org/10.1103/PhysRevB.95.035125