Spin–Orbit Effect on the Molecular Properties of TeX_<i>n</i> (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_<i>n</i> (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 TeI₂ that matches the experimental value. On the basis of the calculated thermochemical energy and optimized molecular structure, TeI₄ 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)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 ⁵Π_g 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 spin-allowed dissociation to the ground states of CrCO and Cr­(CO)₂ with the same spin multiplicities

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

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 SiH₄ to a structure with two bridging H atoms (Si­(μ-H₂)­BH₂, silicon tetrahydroborate). On the basis of the calculated results, this reaction mechanism includes both thermal and photochemical reactions. Especially, thermal conversion of silylene dihydroborate (H₂BSiH₂) to Si­(μ-H₂)­BH₂ 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 H₂BSiH₂ and Si­(μ-H₂)­BH₂ have been identified. Two successive conical intersections (CIs) are involved in the photochemical reaction. The BSiH₄ bending coordinate is almost parallel to the reaction coordinate near the regions from the second CI to Si­(μ-H₂)­BH₂. The activated BSiH₄ bending mode lift the degeneracy of the second CI, thereby the reaction readily proceeds to Si­(μ-H₂)­BH₂. All calculated results in this work reasonably well describe the recent experimental observations

Ab Initio Investigation of the Ground States of F₂P(S)N, F₂PNS, and F₂PSN

A recent spectroscopic experiment identified difluorothiophosphoryl nitrene (F₂P­(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 (F₂PNS). In this work, we identify that the global minimum of the system is the triplet state of F₂PNS, which allows us to explain the inconsistency between the experimental and theoretical results. All calculated results give consistent results with the recent experimental results

Dynamics of Local Chirality during SWCNT Growth: Armchair versus Zigzag Nanotubes

We present an analysis of the dynamics of single-walled carbon nanotube (SWCNT) chirality during growth, using the recently developed local chirality index (LOCI) method [Kim et al. Phys. Rev. Lett. 2011, 107, 175505] in conjunction with quantum chemical molecular dynamics (QM/MD) simulations. Using (5,5) and (8,0) SWCNT fragments attached to an Fe₃₈ catalyst nanoparticle, growth was induced by periodically placing carbon atoms at the edge of the SWCNT. For both armchair and zigzag SWCNTs, QM/MD simulations indicate that defect healingthe process of defect removal during growthis a necessary, but not sufficient, condition for chirality-controlled SWCNT growth. Time-evolution LOCI analysis shows that healing, while restoring the pristine hexagon structure of the growing SWCNT, also leads to changes in the local chirality of the SWCNT edge region and thus of the entire SWCNT itself. In this respect, we show that zigzag SWCNTs are significantly inferior in maintaining their chirality during growth compared to armchair SWCNTs

Performance of Density Functional Theory and Relativistic Effective Core Potential for Ru-Based Organometallic Complexes

Herein a performance assessment of density functionals used for calculating the structural and energetic parameters of bi- and trimetallic Ru-containing organometallic complexes has been performed. The performance of four popular relativistic effective core potentials (RECPs) has also been assessed. On the basis of the calculated results, the MN12-SX (range-separated hybrid functional) demonstrates good performance for calculating the molecular structures, while MN12-L (local functional) performs well for calculating the energetics, including that of the Ru–Ru bond breaking process. The choice of appropriate density functional is a crucial factor for calculating the energetics. The LANL08 demonstrates the lowest performance of the RECPs for calculating the molecular structures, especially the Ru–Ru bond length

Density Functional Theory Assessment of Molecular Structures and Energies of Neutral and Anionic Al_<i>n</i> (<i>n</i> = 2–10) Clusters

We report the results of a benchmarking study on hybrid, hybrid-meta, long-range-corrected, meta-generalized gradient approximation (meta-GGA), and GGA density functional theory (DFT) methods for aluminum (Al) clusters. A range of DFT functionals, such as B3LYP, B1B95, PBE0, mPW1PW91, M06, M06-2X, ωB97X, ωB97XD, TPSSh, BLYP, PBE, mPWPW91, M06-L, and TPSS, have been used to optimize the molecular structures and calculate the vibrational frequencies and four energetic parameters for neutral and anionic Al_<i>n</i> (<i>n</i> = 2–10) clusters. The performances of these functionals are assessed systematically by calculating the vertical ionization energy for neutral Al clusters and the vertical electron detachment energy for anionic Al clusters, along with the cohesive energy and dissociation energy. The results are compared with the available experimental and high-level ab initio calculated results. The calculated results showed that the PBE0 and mPW1PW91 functionals generally provide better results than the other functionals studied. TPSS can be a good choice for the calculations of very large Al clusters. On the other hand, the B3LYP, BLYP, and M06-L functionals are in poor agreement with the available experimental and theoretical results. The calculated results suggest that the hybrid DFT functionals like B3LYP do not always provide better performance than GGA functionals

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

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