Optimized long-range corrected density functionals for electronic and optical properties of bare and ligated CdSe quantum dots

TL;DR

This paper demonstrates that optimally tuned long-range corrected density functionals significantly improve the prediction of optical and fundamental gaps in CdSe quantum dots, outperforming standard functionals like PBE and B3LYP.

Contribution

It introduces a method for tuning long-range corrected functionals specifically for quantum dots, enhancing the accuracy of electronic and optical property predictions.

Findings

Optimized range separation parameters differ for bare and ligated quantum dots.

Tuned functionals yield larger gaps and exciton binding energies than standard functionals.

Localized transitions do not require long-range charge transfer character for accurate predictions.

Abstract

The reliable prediction of optical and fundamental gaps of finite size systems using density functional theory requires to account for the potential self-interaction error, which is notorious for degrading the description of charge transfer transitions. One solution is provided by parameterized long-range corrected functionals such as LC-BLYP, which can be tuned such as to describe certain properties of the particular system at hand. Here, bare and 3-mercaptoprotionic acid covered \ce{Cd33Se33} quantum dots are investigated using the optimally tuned LC-BLYP functional. The range separation parameter, which determines the switching on of the exact exchange contribution is found to be 0.12 bohr$^{-1}$ and 0.09 bohr$^{-1}$ for the bare and covered quantum dot, respectively. It is shown that density functional optimization indeed yields optical and fundamental gaps and thus exciton binding energies, considerably different compared with standard functionals such as the popular PBE and B3LYP ones. This holds true, despite the fact that the leading transitions are localized on the quantum dot and do not show pronounced long-range charge transfer character.