Electronic Structure of Ligated CdSe Clusters: Dependence on DFT Methodology

Abstract

Simulations of ligated semiconductor quantum dots (QDs) and their physical properties, such as morphologies, QDÀligand interactions, electronic structures, and optical transitions, are expected to be very sensitive to computational methodology. We utilize Density Functional Theory (DFT) and systematically study how the choice of density functional, atom-localized basis set, and a solvent affects the physical properties of the Cd 33 Se 33 cluster ligated with a trimethylphosphine oxide ligand. We have found that qualitative performance of all exchange-correlation (XC) functionals is relatively similar in predicting strong QDÀligand binding energy (∼1 eV). Additionally, all functionals predict shorter CdÀSe bond lengths on the QD surface than in its core, revealing the nature and degree of QD surface reconstruction. For proper modeling of geometries and QDÀligand interactions, however, augmentation of even a moderately sized basis set with polarization functions (e.g., LANL2DZ* and 6-31G*) is very important. A polar solvent has very significant implications for the ligand binding energy, decreasing it to 0.2À0.5 eV. However, the solvent model has a minor effect on the optoelectronic properties, resulting in persistent blue shifts up to ∼0.3 eV of the low-energy optical transitions. For obtaining reasonable energy gaps and optical transition energies, hybrid XC functionals augmented by a long-range HartreeÀFock orbital exchange have to be applied.

Functional Assessment for Predicting Charge-Transfer Excitations of Dyes in Complexed State: A Study of Triphenylamine–Donor Dyes on Titania for Dye-Sensitized Solar Cells

“…of the dye to the nanoparticle increases as one goes from B3LYP to CAM-B3LYP, owing to a larger amount of HF-exchange at long range in the latter. 48 Both functionals, however, show the same trend in the binding energies of the three dyes -the L1…”

Effect of Capping Ligands and TiO2 Supporting on the Optical Properties of a (CdSe)13 Cluster

“…Most commonly, to calculate the electronic spectra to study optical properties of QDs, the linear response time-dependent density functional theory (LR-TDDFT) approach 22 is used. 11,18,23 Again, the DFT functional employed plays a key role, and the reader is referred to the benchmark work recently reported by Azpiroz et al 21 Moreover, solvent effects were found to have only a little influence on the absorption spectrum of CdSe QDs, blue-shifting it by 0.2−0.4 eV. 18,21,24 Recently, it was shown that real-time propagation of the wave function in the time domain (RT-TDDFT) is a convenient alternative in the computation of the absorption spectra of organic dyes used in solar cells (DSSC).…”

Quantum Dots and Their Ligand Passivation

“…Among many available ligands coupled to CdSe QDs [40][41][42][43][44][45], trimethyl phosphine oxide (TMPO) and its derivatives (i.e., OPMe 2 (CH 2 ) n Me, n = 0, 1-3) stand out due to their high ligand exchange capacity on the CdSe surface [46]. Zhou and coworkers [35] investigated the passivation effect of these TMPO ligands to (CdSe) 13 using the first-principle density functional theory (DFT), which has been proven as a useful methodology for the study of similar quantum systems [30][31][32][40][41][42][43][44][45][46][47][48][49][50][51]. Figure 8.1 shows the system simulated by Zhou and coworkers.…”

“…The passivation is also inevitable in stabilizing and dispersing QDs in an aggregation-prone aqueous medium, where the organic layer reduces the highly reactive surface potential [30][31][32], which is an intrinsic property of colloidal semiconductor nanoparticles due to high curvature [19,20]. As such, the surface modification is accompanied by its critical influence on the chemical and electronic structures of QDs [11,16].…”

“…As such, the surface modification is accompanied by its critical influence on the chemical and electronic structures of QDs [11,16]. Recent theoretical studies show that the passivating ligands can form stable coordination on QD surface, sustaining the chemical structure of the QD [30][31][32]. On the other hand, experimental study (e.g., PbSe-QD) revealed a complex behavior of the PbSe-QD core interacting with passivating organic layer in controlling the optical property [33].…”