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Do Practical Standard Coupled Cluster Calculations Agree Better than Kohn–Sham Calculations with Currently Available Functionals When Compared to the Best Available Experimental Data for Dissociation Energies of Bonds to 3d Transition Metals?
Coupled-cluster (CC) methods have been extensively used as the high-level approach in quantum electronic structure theory to predict various properties of molecules when experimental results are unavailable. It is often assumed that CC methods, if they include at least up to connected-triple-excitation quasiperturbative corrections to a full treatment of single and double excitations (in particular, CCSD(T)), and a very large basis set, are more accurate than Kohn–Sham (KS) density functional theory (DFT). In the present work, we tested and compared the performance of standard CC and KS methods on bond energy calculations of 20 3d transition metal-containing diatomic molecules against the most reliable experimental data available, as collected in a database called 3dMLBE20. It is found that, although the CCSD(T) and higher levels CC methods have mean unsigned deviations from experiment that are smaller than most exchange-correlation functionals for metal–ligand bond energies of transition metals, the improvement is less than one standard deviation of the mean unsigned deviation. Furthermore, on average, almost half of the 42 exchange-correlation functionals that we tested are closer to experiment than CCSD(T) with the same extended basis set for the same molecule. The results show that, when both relativistic and core–valence correlation effects are considered, even the very high-level (expensive) CC method with single, double, triple, and perturbative quadruple cluster operators, namely, CCSDT(2)Q, averaged over 20 bond energies, gives a mean unsigned deviation (MUD(20) = 4.7 kcal/mol when one correlates only valence, 3p, and 3s electrons of transition metals and only valence electrons of ligands, or 4.6 kcal/mol when one correlates all core electrons except for 1s shells of transition metals, S, and Cl); and that is similar to some good xc functionals (e.g., B97-1 (MUD(20) = 4.5 kcal/mol) and PW6B95 (MUD(20) = 4.9 kcal/mol)) when the same basis set is used. We found that, for both coupled cluster calculations and KS calculations, the T1 diagnostics correlate the errors better than either the M diagnostics or the B1 DFT-based diagnostics. The potential use of practical standard CC methods as a benchmark theory is further confounded by the finding that CC and DFT methods usually have different signs of the error. We conclude that the available experimental data do not provide a justification for using conventional single-reference CC theory calculations to validate or test xc functionals for systems involving 3d transition metals.
Benchmark Calculations for Bond Dissociation Enthalpies of Unsaturated Methyl Esters and the Bond Dissociation Enthalpies of Methyl Linolenate
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Density Functional Theory Study of the Adsorption and Dissociation of Copper(I) Acetamidinates on Ni(110): The Effect of the Substrate
In order to assess the role of a metal substrates on the thermal chemistry of adsorbed acetamidinate metalorganic compounds, we have studied the surface chemistry of copper(I)–N,N'-dimethylacetamidinate on Ni(110) using density functional theory and contrasted it with similar calculations we previously carried out on Cu(110). At low coverages, it was found that, in its most stable configuration, the molecular adsorption of copper(I)–N,N'-dimethylacetamidinate dimers occurs with the Cu atoms occupying surface hollow sites. In this work, the ligands reorient away from those metal centers, and the N atoms develop new direct bonds with surface Ni atoms. However, this configuration is not stable and decomposes by losing both ligands to the surface. In the final state, the two ligands bind via their N atoms to Ni sites one lattice space away from the sites where the Cu atoms remain, with their molecular planes perpendicular to that of the surface. This is in contrast with what happens in the case of adsorption on Cu(110), where the Cu atoms from the metalorganic complex still occupy hollow sites but where only one of the ligands breaks away and binds directly to the surface; the other remains on top of the two Cu ions. In terms of the energetics of adsorption and decomposition, the reactions on Ni(110) are much more exothermic than on Cu(110). Further analysis of the distribution of charge within the adsorbates shows a minor reduction of the Cu atoms of the dimer upon interaction with the surface; full reduction to metallic copper is complete only when both ligands have fully migrated to their new Ni surface sites.
INFLUENCE OF EXCITON DIFFUSION AND CHARGE-TRANSFER STATE DISSOCIATION EFFICIENCY ON THE SHORT-CIRCUIT CURRENT DENSITIES IN SEMI-RANDOM DONOR/ACCEPTOR POLYMER:FULLERENE SOLAR CELLS
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Dispersion forces play a role in (Me 2 IPr)Fe(✓NAd)R 2 (Ad = adamantyl; R = neo Pe, 1-nor) insertions and Fe–R bond dissociation enthalpies (BDEs)
Calculations show that dispersion forces in four-coordinate (Me 2 IPr)Fe(✓NAd)(1-nor) 2 ( 2b ) contribute to greater D(FeR) and subtly slow its migratory insertion relative to the neopentyl analogue.
Dissociative electron attachment induced ring opening in five-membered heterocyclic compounds
Ring opening in five-membered rings induced by gentle impact of low energy electrons.
The balance of electric field and interfacial catalysis in promoting water dissociation in bipolar membranes
Bipolar membranes maintain a steady pH in electrolytic cells through water autodissociation at the interface between their cation- and anion-exchange layers. We analyze the balance of electric field and catalysis in accelerating this reaction.
Determination of the Mg 36 ( n , γ ) Mg 37 reaction rate from Coulomb dissociation of Mg 37
Not Available
Mode Specific Electronic Friction in Dissociative Chemisorption on Metal Surfaces: H 2 on Ag(111)
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Activated mitochondrial apoptosis in hESCs after dissociation involving the PKA/p-p53/Bax signaling pathway
Highlights: • hESC dissociation causes mitochondrial apoptosis. • H89 and Pifithrin α suppress dissociation-induced mitochondrial apoptosis. • PKA/p-p53/Bax signaling pathway is involved in dissociation-induced hESC apoptosis. Human embryonic stem cells (hESCs) are highly fragile with massive cell death after dissociation into single cells, which seriously hampers their applications. The mechanism underlying the massive cell death after dissociation still remains elusive. Here, the expression of apoptosis-related proteins, cell survival and mitochondrial membrane potential in dissociated hESCs before and after the treatments with a protein kinase A (PKA) inhibitor H89 and p53 inhibitor Pifithrin α were investigated, respectively. Protein interactions were identified by immunoprecipitation and immunofluorescence. The results show that the dissociation causes Caspase-dependent apoptosis in hESCs mediated by mitochondrial pathway with the up-regulation of pro-apoptotic proteins, decrease in mitochondrial membrane potential and elevation in pro-apoptotic Cyto c release, which are obviously suppresses by H89. The dissociation-induced increase of phosphorylated p53 Ser15 (p-p53) is suppressed by Pifithrin α which also rescues the elevated levels of pro-apoptotic proteins in mitochondrial pathway. During the dissociation-induced apoptosis, PKA/p-p53/Bax signaling pathway is identified by immunoprecipitation and immunofluorescence showing the most likely interaction between them. These results indicate that dissociation induces mitochondrial apoptosis in hESCs involving PKA/p-p53/Bax signaling pathway, which not only give new insights into the apoptosis mechanism of dissociated hESCs, but also provide clues for developing potential strategies to promote hESC survival after dissociation.
Dissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging
Dissociative photoionization of methyl bromide (CH{sub 3}Br) in an excitation energy range of 10.45–16.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X{sup 2}E of CH{sub 3}Br{sup +} is stable, and both A{sup 2}A{sub 1} and B{sup 2}E ionic excited states are fully dissociative to produce the unique fragment ion of CH{sub 3}{sup +}. From TPEPICO 3D time-sliced velocity images of CH{sub 3}{sup +} dissociated from specific state-selected CH{sub 3}Br{sup +} ion, kinetic energy release distribution (KERD) and angular distribution of CH{sub 3}{sup +} fragment ion are directly obtained. Both spin-orbit states of Br({sup 2}P) atom can be clearly observed in fast dissociation of CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion along C–Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH{sub 3}Br{sup +}(B{sup 2}E) ion. With the aid of the re-calculated potential energy curves of CH{sub 3}Br{sup +} including spin-orbit coupling, dissociation mechanisms of CH{sub 3}Br{sup +} ion in A{sup 2}A{sub 1} and B{sup 2}E states along C–Br rupture are revealed. For CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion, the CH{sub 3}{sup +} + Br({sup 2}P{sub 1/2}) channel is occurred via an adiabatic dissociation by vibration, while the Br({sup 2}P{sub 3/2}) formation is through vibronic coupling to the high vibrational level of X{sup 2}E state followed by rapid dissociation. C–Br bond breaking of CH{sub 3}Br{sup +}(B{sup 2}E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.
Dissociation of H{sub 2} on carbon doped aluminum cluster Al{sub 6}C
The dissociation of H{sub 2} molecule is the first step for chemical storage of hydrogen, and the energy barrier of the dissociation is the key factor to decide the kinetics of the regeneration of the storage material. As a light element, aluminum is an important candidate component for storage materials with high gravimetric density. This paper investigates the adsorption and dissociation of H{sub 2} on carbon doping aluminum cluster Al{sub 6}C. The study shows that doping carbon into aluminum cluster can significantly change the electronic structure and increase the stability. Al{sub 6}C has a few stable isomers with close energies and their structures are quite flexible. The molecular adsorption of H{sub 2} on Al{sub 6}C is very weak, but the H{sub 2} molecule can be dissociated easily on this cluster. The stable product of the dissociated adsorption is searched and the different paths for the dissociation are investigated. During the dissociation of H{sub 2}, the structure of the cluster adjusts accordingly, and strong orbital interaction between the hydrogen and the cluster occurs. The calculated energy barrier for the dissociation is only 0.30 eV, which means the dissociation can take place at moderate temperatures.
Dissociation path competition of radiolysis ionization-induced molecule damage under electron beam illumination
Radiolysis ionization under electron beam illumination induces dissociation and damage of organic and biological molecules; thus, it is impossible to image the related materials by transmission electron microscopy (TEM). To understand the atomistic mechanism of radiolysis damage, we developed a systematical procedure based on real-time time-dependent density functional theory (rt-TDDFT) for simulating the radiolysis damage processes of molecules; this procedure can describe the ionization cross sections of the electronic states and the fast dissociation processes caused by hot carrier cooling and the Auger decay on deep levels. For the radiolysis damage of C 2 H 6 O 2 , our simulation unexpectedly showed that there is strong competition among three different dissociation paths, including fast dissociation caused by nonadiabatic cooling of the hot carrier; fast dissociation caused by Auger decay, which induces double ionization and Coulomb explosion; and slow dissociation caused by increased kinetic energy. As the energy of the incident electron beam changes, the time scales of these dissociation paths and their relative contributions to the molecule damage change significantly. These simulation results explain the measured mass spectra of the C 2 H 6 O 2 dissociation fragments and also provide clear competition mechanisms for blocking these dissociation paths in the TEM imaging of organic and biological materials.
Infrared Laser-Induced Isotope-Selective Dissociation of Molecular van der Waals (SF{sub 6}){sub m}Ar{sub n} Clusters
The results of studies on the isotope-selective dissociation of homogeneous and mixed van der Waals (SF{sub 6}){sub m}Ar{sub n} clusters induced by infrared laser radiation are presented. The method is based on the selective vibrational excitation of clusters by an infrared laser, which leads to their heating and dissociation. An experimental setup and procedure are described. The results of measurements of the efficiency and selectivity of cluster dissociation at different pressures and gas compositions above the nozzle, as well as various parameters of laser radiation, are presented. The dependences of the efficiency and selectivity of cluster dissociation on the frequency and power of the exciting laser radiation on the composition and pressure of gas above the nozzle, as well as on the distance of the irradiation zone of the particles on the nozzle exit are obtained. It is shown that the frequency of laser radiation and the composition and pressure of gas above the nozzle significantly affect the parameters of selective infrared dissociation of clusters. Experiments on isotope-selective dissociation of both homogeneous (SF{sub 6}){sub m} clusters and mixed (SF{sub 6}){sub m}Ar{sub n} clusters are performed. It was found that, with the dissociation of (SF{sub 6}){sub m}Ar{sub n} clusters, a rather high selectivity can be reached. Thus, in the case of an SF{sub 6}/Ar mixture at a pressure ratio of 1/200, for the selectivity of dissociation of ({sup 32}SF{sub 6}){sub 2} clusters with respect to {sup 34}SF{sub 6}{sup 32}SF{sub 6} clusters, the values ≥10–20 are obtained under conditions of irradiation by a beam on the 10P(32) laser line (at a frequency of 932.96 cm{sup –1}). Conditions are found when the values of efficiency and selectivity of dissociation of homogeneous (SF{sub 6}){sub m} clusters and mixed (SF{sub 6}){sub m}Ar{sub n} clusters are optimal.