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

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

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

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