Second-Row Transition-Metal Doping of (ZniSi), i = 12, 16 Nanoclusters: Structural and Magnetic Properties

TM@ZniSi nanoclusters have been characterized by means of the Density Functional Theory, in which Transition Metal (TM) stands from Y to Cd, and i = 12 and 16. These two nanoclusters have been chosen owing to their highly spheroidal shape which allow for favored endohedral structures as compared to other nanoclusters. Doping with TM is chosen due to their magnetic properties. In similar cluster-assembled materials, these magnetic properties are related to the Transition Metal-Transition Metal (TM-TM) distances. At this point, endohedral doping presents a clear advantage over substitutional or exohedral doping, since in the cluster-assembled materials, these TM would occupy the well-fixed center of the cluster, providing in this way a better TM-TM distance control to experimentalists. In addition to endohedral compounds, surface structures and the TS’s connecting both isomers have been characterized. In this way the kinetic and thermal stability of endohedral nanoclusters is predicted. We anticipate that silver and cadmium endohedrally doped nanoclusters have the longest life-times. This is due to the weak interaction of these metals with the cage, in contrast to the remaining cases where the TM covalently bond to a region of the cage. The open-shell electronic structure of Ag provides magnetic properties to Ag@ZniSi clusters. Therefore, we have further characterized (Ag@Zn12S12)2 and (Ag@Zn16S16)2 dimers both in the ferromagnetic and antiferromagnetic state, in order to calculate the corresponding magnetic exchange coupling constant, J.This research was funded by Eusko Jaurlaritza (the Basque Government), and the Spanish Office for Scientific Research. The SGI/IZO-SGIker UPV/EHU (supported by Fondo Social Europeo and MCyT) is gratefully acknowledged for generous allocation of computational resources. JMM would like to thank Spanish Ministry of Science and Innovation for funding through a Ramon y Cajal fellow position (RYC 2008-03216). We thanks Elixabete Rezabal for cheerful discussion

Time-Resolved Chemical Bonding Structure Evolution by Direct-Dynamics Chemical Simulations

Direct-dynamics simulations monitor atomic nuclei trajectories during chemical reactions, where chemical bonds are broken and new ones are formed. While they provide valuable information about the ongoing nuclear dynamics, the evolution of the chemical bonds is customarily overlooked, thus, hindering key information about the reaction mechanism. Here we examine the evolution of the chemical bonds for the three main mechanisms of the F– + CH3CH2Cl reaction using quasi-classical trajectories for the nuclei, and global natural orbitals for the electrons. Key findings include (i) bimolecular nucleophilic substitution (SN2) resembles a one-step bond breaking and formation process; (ii) the elimination mechanisms (syn- and anti-E2) feature a sequential two-step process of proton abstraction and Cl– elimination; and (iii) the anti-E2 mechanism is slower, exhibits rebound effects, and gets activated by specific vibrational modes. This study highlights the importance of correctly describing and thoroughly analyzing the dynamical evolution of chemical bonds for chemical reaction mechanistic studies.Financial support comes from the Eusko Jaurlaritza (Basque Government), ref.: IT1584-22 and from the Grant No. PID 2021-126714NB-I00, funded by MCIN/AEI/10.13039/ 501100011033. The authors are thankful for technical and human support provided by IZO-SGI SGIker of UPV/EHU and DIPC

Structure and Stability of the Endohedrally Doped (X@CdS) X=Na,K,Cl,Br Nanoclusters.

Endohedral (X@CdiSi)q=0,±1 structures have been characterized by means of the density functional theory with X being alkali metals such as Na and K or halogens such as Cl and Br and with i = 4, 9, 12, 15, 16. These nanoclusters have been chosen because of their high sphericity, which is known to be one of the parameters determining the stability of the endohedral nanoclusters, along with the charge and size of the guest atom. In these structures, the atoms are trapped inside previously characterized spheroid hollow structures with positively charged Cd atoms and negatively charged S atoms. Moreover, although the radii of all atoms are similar, Cd atoms are located more inside the structure. For alkali metals, neutral and cationic endohedral compounds have been characterized and, for halogens, neutral and anionic nanoclusters have been characterized. It is observed that some of these guest atoms are trapped in the center of mass of the cluster, while others are found to be displaced from that center leading to structures where the guest atom presents a complex dynamical behavior. This fact was confirmed by quantum molecular dynamics calculations, which further confirmed the thermal stability of these endohedral compounds.This research was funded by EuskoJaurlaritza (the Basque Government) SAIOTEK program.J.M.M. would like to thank the Spanish Ministry of Science and Innovation for funding through a “Ramon y Cajal” Fellowship. The SGI/IZO-SGIker UPV/EHU (supported by Fondo Social Europeo and MCyT) is gratefully acknowledgedfor generous allocation of computational resources

Self-assembling endohedrally doped CdS nanoclusters: new porous solid phases of CdS

Hollow CdS nanoclusters were predicted to trap alkali metals and halogen atoms inside their cavity. Furthermore, electron affinities (EA) of endohedrally halogen doped clusters and ionization potentials (IE) of endohedrally alkali doped clusters were predicted to be very similar. This makes them suitable to build cluster-assembled materials, in the same vein as do related ZnO, ZnS and MgO nanoclusters, which yield porous solid materials. With this aim in mind, we have focused on the assembly of bare CdiSi and endohedral K@CdiSi–X@CdiSi (i = 12, 16, X = Cl, Br) clusters in order to obtain solids with tailored semiconducting and structural properties. Since these hollow nanoclusters possess square and hexagonal faces, three different orientations have to be considered, namely, edge-to-edge (E–E), square-to-square (S–S) and hexagon-to-hexagon (H–H). These three orientations lead to distinct zeolite-like nanoporous bulk CdS solid phases denoted as SOD, LTA and FAU. These solids are low-density crystalline nanoporous materials that might be useful in a wide range of applications ranging from molecular sieves for heterogeneous catalysis to gas storage templates.Financial support comes from Eusko Jaurlaritza and the Spanish Office Scientific Research. The SGI/IZO-SGIker UPV/EHU is gratefully acknowledged for generous allocation of computational resources. JMM would like to thank Spanish Ministry of Science and Innovation for funding through a Ramon y Cajal fellow position (RYC 2008-03216). EJ-I would like to thank the Basque Government for a doctoral grant

Thermal Stability of Endohedral First-Row Transition-Metal TM@ZniSi Structures, i = 12, 16

The thermal stability of first-row transition-metal-doped TM@ZniSi nanoclusters, in which TM stands for the first-row transition metals from Sc to Zn and i = 12, 16, has been analyzed for the two lowest-lying spin states of each metal. These structures were previously characterized by Matxain et al. (Chem.—Eur. J.2008, 14, 8547). We have seen that the metal atom can move toward the surface of the nanocluster, forming the so-called surface-doped structure. Hence, we have calculated the relative energies between these two isomers. Additionally, we have also characterized the transition states connecting both isomers and the energy barriers needed to move from one to another in order to predict the thermal stability of the endohedral compounds. These values are further used to predict the lifetimes of the endohedrally doped nanoclusters. Most of the lifetimes are predicted to be very small, although most of them are large enough for experimental detection. Conversely, the lifetimes of Zn@Zn12S12 and Zn@Zn16S16 have proved to be very large

The natural orbital functional theory of the bonding in Cr2, Mo2 and W2

In this paper, we present for the first time a description based on the natural orbital functional theory (NOFT) of the group VI dimers, namely, Cr2, Mo2 and W2. The PNOF5, Piris Natural Orbital Functional, has been used throughout this work, and the results are compared to multireferential perturbation theory (CASPT2) results. Both methods have been combined with effective core potentials to take into account the scalar relativistic effects. In addition, for Cr2, an all-electron TZVP quality basis set has also been used to recover the core-valence dynamical correlation. In all cases, PNOF5 shows better behavior than CASPT2, which needs a larger basis set to recover comparable amounts of dynamical correlation. PNOF5 is able to account for the non-dynamical electron correlation, which is responsible for the multireferential nature of these dimers. However, it does not fully recover the dynamical correlation, which is crucial for the accurate description of these challenging potential energy curves. Consequently, PNOF5 predicts longer equilibrium distances and lower dissociation energies than the experimental values. Unlike CASPT2, the PNOF5 results do not improve by using larger basis sets. These new findings represent a major step in the NOFT development, since PNOF5 is the first functional of the natural orbitals reported to yield a chemically balanced and accurate description of these challenging transition metal dimers.This research was funded by Eusko Jaurlaritza (the Basque Government) (GIC 07/85 IT-330-07) and the Spanish Office for Scientific Research (CTQ2011-27374). Technical and human support provided by IZO-SGI, SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) is gratefully acknowledged for assistance and generous allocation of computational resources. JMM would like to thank Spanish Ministry of Science and Innovation for funding through a Ramón y Cajal fellow position (RYC 2008-03216)