The higher order (HO) correlation beyond the coupled-cluster single double (triple) CCSD(T) level of theory, second-order spin-orbit coupling (SOC), and core-valence (CV) correlation effects on bond length, r, vibrational frequency, ω, and dissociation energy, D, are studied for a set of 17 lanthanide containing diatomics, including lanthanum, europium, ytterbium, and lutetium oxides and halides. Convergence in the magnitudes of the SOC, CV, and HO corrections with respect to basis set size is examined using a sequence of double, triple, and quadruple-ζ basis sets, with the complete basis set (CBS) limit estimates provided in most cases. The CV effects on D, r, and ω are calculated to amount up to 1.3 kcal·mol, 0.008 Å, and 5 cm, respectively. A detailed analysis of the origin of the CV effect with a particular accounting for various subvalence shells reveals that, generally, the Ln 4d correlation makes a major contribution, although in some instances the lower-lying 4sp shells contribute largely and even more substantially than 4d. The second-order SOC effect evaluated via two-component and four-component relativistic techniques proves to be non-negligible, especially for heavier species, e.g., LaI, in which it is as large as 0.8 kcal·mol in D, 0.002 Å in r, and 1.3 cm in ω. Higher order correlation effects assessed through the CCSDT(Q) level are mostly less than 0.8 kcal·mol, 0.004 Å, and 5 cm; however, in species with prominence of nondynamical correlation, e.g., EuO, YbF, and LuO, the HO correction can amount to 1.2-1.6 kcal·mol, 0.005-0.008 Å, and 8-30 cm in D, r, and ω, respectively. In general, the [CCSD(T)+CV]/CBS + SOC + HO composite results are in good agreement with the available experimental data, exhibiting a mean absolute deviation of 1.8 kcal·mol in D, 0.0023 Å in r, and 3.5 cm in ω. A significant experimental outlier, the bond length in YbI, is revealed, implying the need for re-examination of the experimental data.

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We report an ab initio study on the spectroscopy of the open-shell diatomic molecule yttrium oxide, YO. The study considers the six lowest doublet states, X 2 Σ + , A 2 ∆, A 2 Π, B 2 Σ + , C 2 Π, D 2 Σ + , and a few higher-lying quartet states using high levels of electronic structure theory and accurate nuclear motion calculations. The coupled cluster singles, doubles, and perturbative triples, CCSD(T), and multireference configuration interaction (MRCI) methods are employed in conjunction with a relativistic pseudopotential on the yttrium atom and a series of correlation-consistent basis sets ranging in size from triple-ζ to quintuple-ζ quality. Core-valence correlation effects are taken into account and complete basis set limit extrapolation is performed for CCSD(T). Spin-orbit coupling is included through the use of both MRCI state-interaction with spinorbit (SI-SO) approach and four-component relativistic equationof-motion CCSD calculations. Using the ab initio data for bond lengths ranging from 1.0 to 2.5 Å, we compute 6 potential energy, 12 spin-orbit, 8 electronic angular momentum, 6 electric dipole moment and 12 transition dipole moment (4 parallel and 8 perpendicular) curves which provide a complete description of the spectroscopy of the system of six lowest doublet states. The DUO nuclear motion program is used to solve the coupled nuclear motion Schrödinger equation for these six electronic states. The spectra of 89 Y 16 O simulated for different temperatures are compared with several available high resolution experimental studies; good agreement is found once minor adjustments are made to the electronic excitation energies.

Publisher's Note: "Approaching the basis set limit for transition metal compounds with highly polar bonds: A benchmark coupledcluster study of the and molecular structures and spectra" ARTICLES YOU MAY BE INTERESTED INApproaching the basis set limit for transition metal compounds with highly polar bonds: A benchmark coupled-cluster study of the and molecular structures and spectra This paper was originally published with an error in the last sentence of the fifth paragraph of the Introduction ͑Sec. I͒. That sentence should have read, "It presents a reasonable compromise between the full CCSDT model, 31 which usually gives results in excellent agreement with those obtained with full configuration interaction but is computationally prohibitive, and the CCSD level, which is much less expensive but does not suffice when rigorous comparison to experiment is required." In addition, there was an error in the running title throughout the printed version of the paper. AIP apologizes for these errors. All online versions of the article have been corrected.