Assessment of Exchange-Correlation Functionals in Reproducing the Structure and Optical Gap of Organic-Protected Gold Nanoclusters

Abstract

Extensive benchmarks of exchange-correlation functionals on real X-ray resolved nanoclusters have been carried out and reported here for the first time. The systems investigated and used for the tests are two undecagold and one Au24+-based nanoclusters stabilized by thiol and phosphine ligands. Time-dependent density-functional theory has been used to compare calculations with experimental data on optical gaps. It has been observed that GGA functionals employing PBE-like correlation (viz., PBE itself, B-PBE, B-P86, and B-PW91) coupled with an improved version of the LANL2DZ pseudopotential and basis set provide accurate results for both the structure and optical gap of gold nanoclusters, at a reasonable computational cost. Good geometries have been also obtained using some global hybrid (e.g., PBE0, B3-P86, mPW1-PW91) and range-separated hybrid (e.g., HSE06) functionals making use of PBE-like correlation, even though they yield optical gaps overestimating the experimental findings up to 0.5 eV. Popular exchange-correlation combinations such as B-LYP and B3-LYP deform cluster geometry during structural optimization, probably due to the LYP correlation. Effects of the stabilizing organic ligands on the properties of metal cores have been probed simulating the nanoclusters at the density-functional level of theory retaining the organic coating. This paper provides a useful contribution to the simulations of structural and optoelectronic properties of larger metal–organic particles suitable for a wide range of nanotechnological applications

Molecular and Electronic Structure of the Cluster [Au8(PPh3)8](NO3)2

“…A HOMO-LUMO gap of 2.21 eV (PBE) was found for [Au 11 (PPh 3 ) 7 Cl 3 ], in good agreement with the optical value of 2.0 eV. [8,20] According to these findings, the HOMO-LUMO gaps determined in this work by TDDFT calculations using the GGA functional PBE seem to describe the HOMO-LUMO gaps of the cations of [Au 8 4 in comparison with the other usAuNPs might be caused by the short peripheral Au-Au distances and the higher number of gold atoms, leading to a more bulk-like electronic structure. [5] …”

“…[20] To analyse and understand the interplay between structural features and the electronic structures of usAuNPs, it would be highly desirable to combine the above-mentioned methods. This has partially been demonstrated for thiol-stabilized Au clusters, such as [Au 25 (SR) 18 ] - [15,21] or [Au 23 {SC(CH 3 ) 3 } 16 ], [22] or for Au clusters with a mixed thiol/phosphine ligand shell, such as [Au 25 (PPh 3 ) 10 (SR) 5 Cl 2 ] 2+ .…”

Magneto-Plasmonic Colloidal Nanoparticles Obtained by Laser Ablation of Nickel and Silver Targets in Water

“…29−31 The latter has been chosen because it provides good structural and spectroscopic properties in metal-hybrid nanoclusters in a reasonable computational time. 32,33 The molecular structures of the adenine complexes with silver or nickel oxide and the corresponding vibrational frequencies were computed adopting tight convergence criteria. By allowing all the parameters to relax, the optimized geometries corresponded to true energy minima, as revealed by the lack of imaginary values in the vibrational mode calculations.…”

Relation of molecular structure to Franck–Condon bands in the visible-light absorption spectra of symmetric cationic cyanine dyes

“…The first problem is the well-known tendency of TD-DFT to overestimate the ES energy of these compounds [41][42][43][44][45][46], resulting in overestimation of the transition energies [47]. These errors originate from the multireference character [48] of the ES, and can be reduced somewhat by use of corrected solvent models and optimally tuned hybrid functionals [49], but the cyanines nevertheless remain a challenge.…”