48 research outputs found
Multireference Ab Initio Study of the Ground and Low-LyingExcited States of Cr(CO)2 and Cr(CO)3
We investigate the ground and low-lying excited states of unsaturated chromium carbonyls, Cr(CO)2 and Cr(CO)3, using multiconfigurational ab initio perturbation theory. Unlike other chromium carbonyls, there are discrepancies between the experiment and theory on the identity of the ground states of Cr(CO)2 and Cr(CO)3. From multireference ab initio calculations considering the full valence orbitals of Cr(CO)2 and Cr(CO)3, the differences in the molecular structures of their various electronic states are explained by the electronic structure analysis. On the basis of the result from CASPT2 and MS-CASPT2 calculations, we propose that the ground states of Cr(CO)2 and Cr(CO)3 are the 5Πg and 1A1 states, respectively, addressing the ambiguity regarding their ground states. In addition, the multiconfigurational ab initio perturbation theory calculations reveal that (1) the energy gaps between the ground and first low-lying excited states of Cr(CO)2 and Cr(CO)3 are quite small and (2) the first low-lying excited states of Cr(CO)2 and Cr(CO)3 have the same spin multiplicities as the ground states of CrCO and Cr(CO)2, respectively, which are the products of ligand dissociation. As a result, the apparent spin-forbidden dissociation of Cr(CO)2 and Cr(CO)3 into CrCO and Cr(CO)2, respectively, are likely to be facilitated by thermal excitation of the ground states of Cr(CO)2 and Cr(CO)3 into their first low-lying excited states, which then actually undergoes the spinallowed dissociation to the ground states of CrCO and Cr(CO)2 with the same spin multiplicities.1221sciescopu
Spin–Orbit Effect on the Molecular Properties of TeX<sub><i>n</i></sub> (X = F, Cl, Br, and I; <i>n</i> = 1, 2, and 4): A Density Functional Theory and Ab Initio Study
Density functional theory (DFT) and
ab initio calculations, including
spin–orbit coupling (SOC), were performed to investigate the
spin–orbit (SO) effect on the molecular properties of tellurium
halides, TeX<sub><i>n</i></sub> (X = F, Cl, Br, and I; <i>n</i> = 1, 2, and 4). SOC elongates the Te–X bond and
slightly reduces the vibrational frequencies. Consideration of SOC
leads to better agreement with experimental values. Møller–Plesset
second-order perturbation theory (MP2) seriously underestimates the
Te–X bond lengths. In contrast, B3LYP significantly overestimates
them. SO-PBE0 and multireference configuration interactions with the
Davidson correction (MRCI+Q), which include SOC via a state-interaction
approach, give the Te–I bond length of TeI<sub>2</sub> that
matches the experimental value. On the basis of the calculated thermochemical
energy and optimized molecular structure, TeI<sub>4</sub> is unlikely
to be stable. The use of PBE0 including SOC is strongly recommended
for predicting the molecular properties of Te-containing compounds
Multireference Ab Initio Study of the Ground and Low-Lying Excited States of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub>
We
investigate the ground and low-lying excited states of unsaturated
chromium carbonyls, Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub>, using
multiconfigurational ab initio perturbation theory. Unlike other chromium
carbonyls, there are discrepancies between the experiment and theory
on the identity of the ground states of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub>. From multireference ab initio calculations considering the
full valence orbitals of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub>, the differences in the molecular structures of their various electronic
states are explained by the electronic structure analysis. On the
basis of the result from CASPT2 and MS-CASPT2 calculations, we propose
that the ground states of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub> are the <sup>5</sup>Π<sub>g</sub> and <sup>1</sup>A<sub>1</sub> states, respectively, addressing the ambiguity regarding their ground
states. In addition, the multiconfigurational ab initio perturbation
theory calculations reveal that (1) the energy gaps between the ground
and first low-lying excited states of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub> are quite small and (2) the first low-lying excited states
of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub> have the same spin multiplicities
as the ground states of CrCO and Cr(CO)<sub>2</sub>, respectively,
which are the products of ligand dissociation. As a result, the apparent
spin-forbidden dissociation of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub> into CrCO and Cr(CO)<sub>2</sub>, respectively, are likely to
be facilitated by thermal excitation of the ground states of Cr(CO)<sub>2</sub> and Cr(CO)<sub>3</sub> into their first low-lying excited states, which then actually undergoes the spin-allowed
dissociation to the ground states of CrCO and Cr(CO)<sub>2</sub> with
the same spin multiplicities
Experimental Study on Ion Transport in Microfluidic Electrodialysis Using Partially Masked Ion Exchange Membranes
Electrodialysis using anion-exchange membranes (AEMs) and cation-exchange membranes (CEMs) has been widely used for water desalination and the management of various ionic species. During commercial electrodialysis, the available area of an ion-exchange membrane is reduced by a non-conductive spacer that is in contact with the AEM/CEM. Although multiple reports have described the advantages or disadvantages of spacers, fewer studies have explored the effects of spacers on the mass transport effect of the reduced membrane area excluding the fluid flow change. In this paper, we present our experimental studies concerning mass transport in microfluidic electrodialysis systems with partially masked ion-exchange membranes. Six different types of masking membranes were prepared by the deposition of non-conductive films on parts of the membranes. The experimental results showed that the overlapped types (in which masking was vertically aligned in the AEM/CEM) exhibited a larger electrical conductance and better current/energy efficiency, compared with the non-overlapped types (in which masking was vertically dislocated in the AEM/CEM). We also observed that a reduction in the unit length of the unmasked ion-exchange membrane enhanced overall mass transport. Our results demonstrate the effects of patterned membranes on electrical resistance and desalination performance; they also identify appropriate arrangements for electromembrane systems
Ab Initio Analysis of Auger-Assisted Electron Transfer
Quantum
confinement in nanoscale materials allows Auger-type electron–hole
energy exchange. We show by direct time-domain atomistic simulation
and analytic theory that Auger processes give rise to a new mechanism
of charge transfer (CT) on the nanoscale. Auger-assisted CT eliminates
the renown Marcus inverted regime, rationalizing recent experiments
on CT from quantum dots to molecular adsorbates. The ab initio simulation
reveals a complex interplay of the electron–hole and charge–phonon
channels of energy exchange, demonstrating a variety of CT scenarios.
The developed Marcus rate theory for Auger-assisted CT describes,
without adjustable parameters, the experimental plateau of the CT
rate in the region of large donor–acceptor energy gap. The
analytic theory and atomistic insights apply broadly to charge and
energy transfer in nanoscale systems
Prospect of Retrieving Vibrational Wave Function by Single-Object Scattering Sampling
The exact shape of wave functions has never been directly measured because an ensemble measurement is often overwhelmed by the contributions of highly populated configurations. In this work, we explore the possibility of directly obtaining vibrational wave functions by single object scattering sampling (SOSS) using intense, ultrashort X-ray pulses provided by X-ray free electron lasers. Previously, single molecule diffraction experiments using femtosecond X-ray pulses have been proposed with the prospect of determining three-dimensional structure of macromolecules without the need of single crystal samples. In contrast to the previous proposals, SOSS is designed for obtaining the structural variations of constantly fluctuating molecules by sampling many single shot, single object scattering patterns From the simulations on iodine molecules adopting various pulse characteristics and molecular parameters, we were able to reconstruct vibrational wave functions of molecular iodine and found that SOSS is feasible under appropriate experimental conditions.112sciescopu
Mechanistic Investigation of Thermal and Photoreactions between Boron and Silane
Density
functional theory and high-level ab initio calculations
were performed to elucidate the detailed reaction mechanism from B
and SiH<sub>4</sub> to a structure with two bridging H atoms (Si(μ-H<sub>2</sub>)BH<sub>2</sub>, silicon tetrahydroborate). On the basis of
the calculated results, this reaction mechanism includes both thermal
and photochemical reactions. Especially, thermal conversion of silylene
dihydroborate (H<sub>2</sub>BSiH<sub>2</sub>) to Si(μ-H<sub>2</sub>)BH<sub>2</sub> is not feasible because two high energetic
barriers must be overcome. In contrast, the reverse reaction is feasible
because it is effectively only necessary to overcome a single barrier.
The characteristics of the excited states of H<sub>2</sub>BSiH<sub>2</sub> and Si(μ-H<sub>2</sub>)BH<sub>2</sub> have been identified.
Two successive conical intersections (CIs) are involved in the photochemical
reaction. The BSiH<sub>4</sub> bending coordinate is almost parallel
to the reaction coordinate near the regions from the second CI to
Si(μ-H<sub>2</sub>)BH<sub>2</sub>. The activated BSiH<sub>4</sub> bending mode lift the degeneracy of the second CI, thereby the reaction
readily proceeds to Si(μ-H<sub>2</sub>)BH<sub>2</sub>. All calculated
results in this work reasonably well describe the recent experimental
observations
Reactivity of molecular oxygen with aluminum clusters: Density functional and Ab Initio molecular dynamics simulation study
Dissociative adsorption of molecular oxygen (O-2) on aluminum (Al) clusters has attracted much interest in the field of surface science and catalysis, but theoretical predictions of the reactivity of this reaction in terms of barrier height is still challenging. In this regard, we systematically investigate the reactivity of O-2 with Al clusters using density functional theory (DFT) and atom-centered density matrix propagation (ADMP) simulations. We also calculate potential energy surfaces (PESs) of the reaction between O-2 and Al clusters to estimate the barrier energy of this reaction. The M06-2X functional gives the barrier energy in agreement with the one calculated by coupled cluster singles and doubles with perturbed triples (CCSD(T)) while the TPSSh functional significantly underestimates the barrier height. The ADMP simulation using the M06-2X functional predicts the reactivity of O-2 with the Al cluster in agreement with the experimental findings, that is, singlet O-2 readily reacts with Al clusters but triplet O-2 is less reactive. We found that the ability of a DFT functional to describe the charge transfer appropriately is critical for calculating the barrier energy and the reactivity of the reaction of O-2 with Al clusters. The M06-2X functional is relevant for investigating chemical reactions involving Al and O-2. (c) 2016 Wiley Periodicals, Inc.11Nsciescopu
Ab Initio Investigation of the Ground States of F<sub>2</sub>P(S)N, F<sub>2</sub>PNS, and F<sub>2</sub>PSN
A recent
spectroscopic experiment identified difluorothiophosphoryl nitrene
(F<sub>2</sub>P(S)N) and found that it showed rich photochemistry.
However, a discrepancy between the experimental results and the quantum
chemical calculations was reported. Thus, high-level ab initio calculations
using the coupled cluster singles and doubles with perturbative triples
and second-order multiconfigurational perturbation theory were performed
to elucidate this inconsistency. The discrepancy arose due to the
failure to consider the triplet state of difluoro(thionitroso)phosphine
(F<sub>2</sub>PNS). In this work, we identify that the global minimum
of the system is the triplet state of F<sub>2</sub>PNS, which allows
us to explain the inconsistency between the experimental and theoretical
results. All calculated results give consistent results with the recent
experimental results
Self-Piercing Riveted Joint of Vibration-Damping Steel and Aluminum Alloy
In this study, the self-piercing rivet (SPR) joining of vibration-damping steel and aluminum alloy (Al5052-H32) is successfully carried out, for the first time to our knowledge, and the effects of die type and joint configuration on the mechanical performance, failure mode, and geometrical characteristics of the new joint are investigated. The vibration-damping steel and Al5052-H32 SPR joint exhibits the largest tensile–shear load when a flat die is used. An increase in the die taper angle and diameter decreases the mechanical performance of the joint due to the increase in volume of the die, leading to a smaller interlock width of the joint. The joint configuration with Al5052-H32 as a top sheet has superior mechanical performance compared with the reverse configuration, owing to the increase of the interlock width. All SPR joints of vibration-damping steel and Al5052-H32 show consistent rivet pull-out failure, regardless of the joint configuration, because of relatively small interlock width. It is also found that these SPR joints show better mechanical performance than those of SPFC590DP (a skin material of the vibration-damping steel) and Al5052-H32 under the Al5052-H32–top configuration