Investigation of Many-Body Correlation in Biexcitonic Systems Using Electron–Hole Multicomponent Coupled-Cluster Theory

Abstract

Generation of biexcitons in semiconductor nanoparticles has important technological applications in designing efficient light-harvesting materials. Like excitons, the attractive electron–hole interaction terms are responsible for binding in biexcitonic systems. However, unlike excitons, electron–electron and hole–hole repulsive components also contribute to the overall interaction in a biexcitonic system. Consequently, a balanced treatment of many-body correlation associated with electron–electron, hole–hole, and electron–hole interactions is needed for understanding quaisparticle binding in biexcitons. This work presents a theoretical investigation of the effect of size and chemical composition on biexciton binding energies in semiconductor nanoparticles using the electron–hole multicomponent coupled-cluster theory (eh-mcCC). Exciton and biexciton binding energies for quantum dots with diameters 1–20 nm for four semiconductor materials (CdSe, CdS, CdTe, and PbS) were calculated using the eh-mcCC method. The calculated exciton and biexciton binding energies were found to be in good agreement with previously reported experimental results for quantum dots. The results from these calculations demonstrate that exciton and biexciton binding energies exhibit very different scaling behavior with respect to increasing dot diameter. Specifically, with increasing dot diameter, exciton binding energies were found to decrease following a power-law dependence. By contrast, the biexciton binding energies were found to decrease exponentially and decreased at a slower rate as compared to exciton binding energies. The dramatic difference between the scaling equations for the exciton and biexciton binding energies shows that the response of the biexcitonic system with respect to change in the confinement potential is fundamentally very different from the response shown by excitonic systems.

Unusually Strong Biexciton Repulsion Detected in Quantum Confined CsPbBr3 Nanocrystals with Two and Three Pulse Femtosecond Spectroscopy

“…The assignment of A2 to extreme blue shifting of the second BE transition poses several riddles. This shift is not only nearly an order of magnitude larger than biexciton interaction energies in other nanocrystals, 36,37 it is also opposite in sign or a repulsion. A similar situation has been observed in type II core/shell nanocrystals and promoted as a means of enhancing optical gain by relieving the overlap of emission and absorption at the mutual BG.…”

Multicomponent CASSCF Revisited: Large Active Spaces Are Needed for Qualitatively Accurate Protonic Densities

“…The percent change in the protonic density error for these two calculations is 1.55 and 1.18 for the FHFand HCN molecules respectively. For the FHFmolecule with a (12,27)/ (1,13) active space, the difference in energy between the two calculations with an ε value of 5.0*10 -5 or 2.5*10 -5 is 0.3 mHa with no change in the density error. For the HCN molecule with an (8,24)/(1,14) active space, the change in energy is 0.3 mHa and the percent change in the protonic density error is 0.37.…”

“…Unfortunately, due to the qualitatively incorrect nature of multicomponent Hartree–Fock, multicomponent extensions of standard single-component methodology such as truncated configuration interaction (CI) with single and doubles excitations or Møller–Plesset second-order perturbation theory − (MP2) are not even qualitatively accurate as the multicomponent Hartree–Fock wave function is not a sufficiently good reference wave function. Multicomponent coupled cluster (CC) theory ,− has been shown to give accurate protonic properties only if single excitations are included in the cluster operator, which is another indication of the poor quality of the multicomponent HF orbitals. Additionally, if excitations up to quadruples are included in a truncated CI expansion (CISDTQ), accurate protonic densities can be obtained …”

Multicomponent Coupled Cluster Singles and Doubles Theory within the Nuclear-Electronic Orbital Framework

“…In this approximation, nuclei are treated classically as point charges during the solution of the time-independent electronic Schrödinger equation. However, many interesting chemical phenomena, such as hydrogen tunneling and proton-coupled electron transfer, require a quantum mechanical description of nuclei beyond the Born–Oppenheimer approximation. − A variety of methods have been developed in an effort to address these issues. − A computationally practical way of accurately incorporating nuclear quantum effects is provided by the nuclear-electronic orbital (NEO) approach . In the NEO framework, select nuclei, typically protons, are treated quantum mechanically on the same level as the electrons, with at least two nuclei treated classically to avoid issues associated with translations and rotations.…”