Revisiting the potential-energy surface of CnBe3n+2H2n+22+ (n = 2-4) clusters: are planar pentacoordinate carbon structures the global minima?

Using various exploration strategies, in this study, we investigated the potential energy surfaces (PES) of CBe5H5+ and CnBe3n+2H2n+22+ (n = 2-4) clusters. Previous studies proposed that the planar pentacoordinate carbons (ppCs) were the global minima of these clusters. However, our study identified new putative global minima and competitive isomers, refuting some previous assignments. We employed several methods, including evolutive-inspired stochastic approaches guided by "chemical criteria", and ab initio molecular dynamics simulations at elevated temperatures. Our results showed that the size of the scanned population significantly affected the evolutive method and that constrained or guided procedures showed an advantage in identifying better minima for larger systems. This study demonstrated that using multiple complementary strategies can result in a wider variety of minima in a given energy range. Our findings provide valuable insights into exploring the potential energy surfaces of clusters, mainly medium-sized clusters, which could be the connections between small clusters and nanomaterials.

Closed-shell d10-d10 mechanochromic [AuPh(CNPh)]n complex: quantum chemistry electronic and optical properties.

The electronic structure, spectroscopic properties, and solid state chemistry of monomer and dimers of [AuPh(CNPh)] complex were studied at post-Hartree-Fock (MP2, SCS-MP2, and CC2) and density functional theory levels. The absorption spectra of these complexes were calculated using single excitation time-dependent (TD) methods at DFT, CC2, and SCS-CC2 levels. The influences of the bulk are accounted for at the PBE-D3 level, incorporating dispersion effects. The calculated values agree with the experimental range, where absorption and emission energies reproduce experimental trends with large Stokes shifts. The aurophilic interaction is identified as a key factor influencing the spectroscopic and structural properties of these complexes. The intermetallic interactions were found as the main factor responsible for MMCT electronic transitions in the models studied.

A relation between different scales of electrophilicity: are the scales consistent along a chemical reaction?

In this paper, a relationship is established between three electrophilicity scales, namely, the electrophilicity index defined by Parr, Liu, and von Szentpaly; the electron affinity; and the energy of the lowest unoccupied molecular orbital (LUMO). Profiles of electrophilicity index and LUMO energies for different kinds of chemical reactions are compared to verify if they remain consistent during a whole chemical process. It appears that the electrophilicity index and the LUMO energies are linearly correlated in almost all the cases. Besides electrophilicity scales, profiles provide valuable information about the charge-transfer stage of a chemical process.

Application of dual descriptor to understand the activity of C u/Z r O 2 catalysts in the water gas shift reaction.

A comparative theoretical study applying Dual Descriptor has been performed using Water Gas Shift reaction, catalyzed by copper supported on monoclinic and tetragonal zirconia. The Dual Descriptor and thermodynamic considerations were used to understand the structural effects that occur in the reaction when it is catalyzed by C u on both zirconia phases. It was found that the formation of carbonates in the C u supported on tetragonal zirconia dehydrogenates consistently with experimental results.

Influence of the monoclinic and tetragonal zirconia phases on the water gas shift reaction. A theoretical study.

We present a theoretical study of the water gas shift reaction taking place on zirconia surfaces modeled by monoclinic and tetragonal clusters. In order to understand the charge transfer between the active species, in this work we analyze the influence of the geometry of monoclinic and tetragonal zirconia using reactivity descriptors such as electronic chemical potential (µ), charge transfer (ΔN) and molecular hardness (η). We have found that the most preferred surface is tetragonal zirconia (tZrO2) indicating also that low charge transfer systems will generate less stable intermediates, that will allow to facilitate desorption process.

The mechanism of methanol decomposition by CuO. A theoretical study based on the reaction force and reaction electronic flux analysis.

A theoretical study of methanol decomposition using a model representing the initial step of the reaction CH3OH + CuO → CH2O + H2O + Cu is presented. Theoretical calculations using B3LYP/6-31 G along with Lanl2DZ pseudopotentials on metallic centers were performed and the results discussed within the framework of the reaction force analysis. It has been found that the reaction takes place following a stepwise mechanism: first, copper reduction (Cu⁺² → Cu⁺) accompanies the oxygen transposition and then a second reduction takes place (Cu⁺ → Cu0) together with a proton transfer that produce formaldehyde and release a water molecule.