Exploration of Free Energy Surface of the Au10 Nanocluster at Finite Temperature

The first step in comprehending the properties of Au10 clusters is understanding the lowest energy structure at low and high temperatures. Functional materials operate at finite temperatures; however, energy computations employing density functional theory (DFT) methodology are typically carried out at zero temperature, leaving many properties unexplored. This study explored the potential and free energy surface of the neutral Au10 nanocluster at a finite temperature, employing a genetic algorithm coupled with DFT and nanothermodynamics. Furthermore, we computed the thermal population and infrared Boltzmann spectrum at a finite temperature and compared it with the validated experimental data. Moreover, we performed the chemical bonding analysis using the quantum theory of atoms in molecules (QTAIM) approach and the adaptive natural density partitioning method (AdNDP) to shed light on the bonding of Au atoms in the low-energy structures. In the calculations, we take into consideration the relativistic effects through the zero-order regular approximation (ZORA), the dispersion through Grimme's dispersion with Becke-Johnson damping (D3BJ), and we employed nanothermodynamics to consider temperature contributions. Small Au clusters prefer the planar shape, and the transition from 2D to 3D could take place at atomic clusters consisting of ten atoms, which could be affected by temperature, relativistic effects, and dispersion. We analyzed the energetic ordering of structures calculated using DFT with ZORA and single-point energy calculation employing the DLPNO-CCSD(T) methodology. Our findings indicate that the planar lowest energy structure computed with DFT is not the lowest energy structure computed at the DLPN0-CCSD(T) level of theory. The computed thermal population indicates that the 2D elongated hexagon configuration strongly dominates at a temperature range of 50-800 K. Based on the thermal population, at a temperature of 100 K, the computed IR Boltzmann spectrum agrees with the experimental IR spectrum. The chemical bonding analysis on the lowest energy structure indicates that the cluster bond is due only to the electrons of the 6 s orbital, and the Au d orbitals do not participate in the bonding of this system.

Unveiling the effect of 2D silagraphene structural diversity on electronic properties: DFT, DOS, and ELF studies

Recently, fully π-functional two-dimensional (2D) materials have been reported for electronic device applications. Graphene is one of these 2D materials that is attributed to 2D electron confinement effects and exhibits an aromatic character; however, it is characterized by vanishing the bandgap energy. Hence, research was focused on the discovery of graphene-based 2D materials to reduce the bandgap energy. Herein, we investigate the silagraphene structures (Si_xC_y) using DFT calculations to undertake and improve structural, physico-chemical, and electronic properties. Various types of 2D networks have been investigated by considering C-C and C-Si bonds in relative positions. Both conjugation and hyperconjugation phenomenon have been deeply examined and it seemed that they take advantage of each other depending on the C-C and C-Si bond positions. Localized orbital locator (LOL) and electron localization function (ELF) were also performed to examine the electronic densities in the investigated 2D networks and unveil the electronic properties of the studied materials.

Cationic gold clusters with eight valence electrons: possible spherical aromatic systems with Sigma holes

The energetically preferred structures of the gold clusters Au9+, Au113+, and Au124+ with eight skeletal electrons have been studied by density functional theory for comparison with the 8-electron Au102+ cluster shown previously to have a highly favored Td tetracapped octahedral structure. The low-energy structures for the Au9+ and Au113+ clusters are found to be similar relatively spherical polyhedra. Such systems can be considered to exhibit spherical aromaticity in accord with their filled 1S21P6 shells, their diatropic NICS(0) values ranging from -21.4 to -44.3 ppm, and their shielding cone surfaces. However, the preferred spherical polyhedra for Au9+ and Au113+ are not the same as the closo deltahedra found in the BnHn2- borane dianions. Instead they have smaller internal cavities formed by capping faces of smaller deltahedra or by formation of internal Au-Au bonds. The lowest energy Au124+ structures are not similar nearly spherical polyhedral structures. Instead they are derived from planar gold subclusters by adding more gold atoms to form tetrahedral Au4 bubbles. The planar origin of the low-energy Au124+ structures relates to the energetic preference for neutral Au<14 clusters for planar structures or nearly planar structures containing small polyhedral bubbles. The presence of σ-holes has been identified on the surfaces of the complete series of the Aun(n-8)+ (n = 9 to 12) clusters. The strength of their electrostatic interactions is predicted to increase upon increasing cluster size.

The adsorption of helium atoms on small cationic gold clusters

Adducts formed between small gold cluster cations and helium atoms are reported for the first time. These binary ions, Aun+Hem, were produced by electron ionization of helium nanodroplets doped with neutral gold clusters and were detected using mass spectrometry. For a given value of n, the distribution of ions as a function of the number of added helium atoms, m, has been recorded. Peaks with anomalously high intensities, corresponding to so-called magic number ions, are identified and interpreted in terms of the geometric structures of the underlying Aun+ ions. These features can be accounted for by planar structures for Aun+ ions with n ≤ 7, with the addition of helium having no significant effect on the structures of the underlying gold cluster ions. According to ion mobility studies and some theoretical predictions, a 3-D structure is expected for Au8+. However, the findings for Au8+ in this work are more consistent with a planar structure.

Exploring the low-lying structures of Aun(CO)+ (n = 1–10): adsorption and stretching frequencies of CO on various coordination sites

Adsorption of CO on cationic gold clusters is insensitive to the structural details of the adsorption site.

Geometric and electronic properties of gold clusters doped with a single oxygen atom

A systematic theoretical study on single oxygen atom doped gold clusters showed that a single oxygen atom can be adsorbed on various sites of gold surfaces, and obtain nearly one electron from gold atoms.