Exciton fine structure in CdSe nanoplatelets using a quasi-2D screened configuration-interaction framework

We compute exciton binding energies and fine-structure splittings in CdSe nanoplatelets with two zincblende geometries and one wurtzite geometry, finding that the wurtzite structure exhibits the largest bright-bright splitting due to its intrinsic in-plane anisotropy, while the zincblende structures show smaller but finite splittings arising from atomistic symmetry breaking at edges and corners. These results are obtained using a theoretical framework that we developed, which combines DFT single-particle states with screened configuration interaction, a quasi-2D dielectric screening model, and an efficient Coulomb-cutoff scheme that eliminates periodic-image interactions and enables accurate Coulomb and exchange integrals at low computational cost. This methodology provides a transferable and practical route for studying excitons in CdSe nanoplatelets and other quasi-two-dimensional nanomaterials.

💡 Research Summary

In this work the authors present a comprehensive first‑principles framework for calculating exciton binding energies and fine‑structure splittings in quasi‑two‑dimensional CdSe nanoplatelets (NPLs). Three representative NPL geometries are examined: two zincblende (ZB) configurations differing in their side‑facet orientation, and one wurtzite (WZ) configuration that exhibits intrinsic in‑plane anisotropy. The central methodological advance lies in the combination of density‑functional theory (DFT) single‑particle states with a screened configuration‑interaction (CI) approach that is specifically adapted to the quasi‑2D nature of NPLs.

The screened electron–hole interaction is modeled using a quasi‑2D dielectric function ε₂D(q∥). The authors adopt the analytical model of Trolle et al., which builds on the three‑dimensional Resta screening function ε₃D(q) and incorporates the physical thickness d of the platelet. This yields a momentum‑space screened Coulomb potential W(q) = 4π ε₂D⁻¹(q∥)/(q∥² + qz²). To evaluate the direct (J) and exchange (K) matrix elements efficiently, the screened potential is Fourier‑transformed to real space, where a specially designed Coulomb‑cut‑off scheme is applied. The cutoff consists of separable in‑plane and out‑of‑plane functions f_in(r∥) and f_out(z) of the form 1/