1,720,994 research outputs found
THEORETICAL INSIGHTS ON O2 AND CO ADSORPTION ON NEUTRAL AND POSITIVELY CHARGED GOLD CLUSTERS
No full textWith the aim of understanding the elementary steps governing the oxidation of CO catalyzed by dispersed or supported gold nanoclusters, the adsorption of molecular species, such as O2 and CO, on model neutral and positively charged clusters (Aun m+ n ) 1, 9, and 13; m ) 0, 1, and 3) has been studied using an ab initio approach. The computed structural and thermodynamic data related to the binding process show that molecular oxygen interacts better with neutral clusters, acting as an electron acceptor, while CO more strongly binds to positively charged species, thus acting as an electron donor
Modeling the Electron Transfer Chain in an Artificial Photosynthetic Machine
No full textThe development of efficient artificial leaves relies on the subtle combination of molecular assemblies able to absorb sunlight, converting light energy into electrochemical potential energy and finally transducing it into accessible chemical energy. The electronic design of these charge transfer molecular machines is crucial to build a complex supramolecular architecture for the light energy conversion. Here, we present an ab initio simulation of the whole decay pathways of a recently proposed artificial molecular reaction center. A complete structural and energetic characterization has been carried out with methods based on density functional theory, its time-dependent version, and a broken-symmetry approach. On the basis of our findings we provide a revision of the pathway only indirectly postulated from an experimental point of view, along with unprecedented and significant insights on the electronic and nuclear structure of intramolecular charge-separated states, which are fundamental for the application of this molecular assembly in photoelectrochemical cells. Importantly, we unravel the molecular driving forces of the various charge transfer steps, in particular those leading to the proton-coupled electron transfer final product, highlighting key elements for the future design strategies of such molecular assays
CO oxidation on cationic gold clusters: A theoretical study
No full textAiming at understanding the elementary steps governing the oxidation of CO catalyzed by dispersed or supported gold nanoclusters, the reactivity of molecular species, such as O2 and CO, on neutral and positively charged Au13 clusters have been studied using a DFT approach. Two CO oxidation mechanisms have been simulated, involving respectively the adsorption of CO and O2 on adjacent catalytic sites (two-sites mechanism) and the competitive interaction of the reactants on the same site (single-site mechanism). It is demonstrated that in the former scheme a definite interaction of CO and O2 with both the charged and neutral cluster is effective, but that a chemical reaction between the adsorbates does not take place. Only the latter mechanism on positively charged Au13 cluster can give rise to the rupture of dioxygen and carbon dioxide formation. Detailed reaction paths corresponding to this case are calculated
Structure and magnetic properties of oxoverdazyl radicals and biradicals by an integrated computational approach
No full textOn calculation and modeling magnetic exchange interactions in weakly bonded systems. The case of the ferromagnetic copper(II) m2-azido bridged complexes
No full textStructure and magnetic properties of oxoverdazyl radicals and biradicals by an integrated computational approach
No full textA DFT investigation of CO oxidation over neutral and cationic gold clusters
No full textThe interaction of CO and O2 with neutral and positively charged Au9 and Au13 clusters was studied using Density Functional Theory. The aim was the understanding of the elementary steps of the low temperature activity of supported gold nanoparticles towards carbon monoxide combustion, that is, the oxidation of CO to CO2 in presence of dioxygen molecules. The adsorption of a single CO molecule gives rise to a substantial electronic rearrangement on both neutral and cationic gold clusters. On the contrary, the adsorption of dioxygen produces an electron transfer from neutral gold clusters to the O2, while the interaction with cationic Au nanoparticles is simply electrostatic. Co-adsorption of CO and O2 on adjacent catalytic sites produces a synergic electronic rearrangement on neutral cluster, but carbon monoxide oxidation does not take place. It is only when the two reactants are forced to interact with the same Au catalytic site that a chemical reaction takes place, leading to the rupture of the O2 molecule on cationic Au13. On a neutral Au13 cluster, on the other hand, the formation of an adduct containing a weakly bound dioxygen and a not fully formed carbon dioxide molecule is observed. The adsorption of a second CO molecule gives rise on both neutral and cationic aggregates to the facile desorption of CO2. Detailed reaction paths and energy barriers are calculated for each CO oxidation process
Metrics for Molecular Electronic Excitations: A Comparison between Orbital- and Density-Based Descriptors
No full textThis study proposes a quantitative and qualitative comparison of two popular metrics used for time-dependent density functional simulations of chromophores when describing absorption and emission processes, with high discrimination power between short- and long-range character of involved electronic excitations and functional performances. To this end, a total of 160 absorption and emission electronic excitations of 80 molecular systems belonging to the "Real-Life Molecules" data set, recently introduced in literature, have been considered a relevant data set. The two selected indexes are based on density (the D-CT one) and natural transition orbitals (the Delta r(NTO) one), respectively. For comparison purposes, an extension of the D-CT index, in line with what exists for Delta r(NTO), enabling to discriminate electronic transitions occurring in syminetric systems is also proposed. The results show that, independently of the exchange and correlation functional used, a good correlation between the natural transition orbital and density based descriptors is found, thus cross validating their use for the quantification of a large variety of transitions in chemically relevant molecular systems
On calculation and modeling magnetic exchange interactions in weakly bonded systems. The case of the ferromagnetic copper(II) m2-azido bridged complexes
No full textChapter 12. Theoretical Insights on the Chemical Reactivity of Metalloporphyrins Using Density Functional Theory
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