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To facilitate the data analysis of current and future high-resolution space telescope missions, we adopt 'Best Theory + Reliable High-resolution Experiment' (BTRHE) strategy to develop highly accurate infrared line lists for nitrous oxide (N2O). The 'Ames-1' potential energy surface (PES) is a CCSD(T)/aug-cc-pVQZ PES refined using selected HITRAN experimental data, with σrms = 0.02–0.03 cm-1 for five isotopologues. The 'Ames-1' dipole moment surface (DMS) is fitted from CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles extrapolated to one electron basis set limit. Using the Ames-1 PES and DMS, Ames-296K line lists are computed in the full range of 0–15,000 cm-1 for 12 N2O isotopologues, with S296K ≥ 10−31 cm-1/molecule.cm-2. The reliability and consistency of Ames-296K intensity predictions (SAmes) are demonstrated through comparisons with HITRAN (SHITRAN), NOSL-296 (SNOSL), recent observed intensities (Sobs) and Effective Dipole Model (EDM) intensities (SEDM). Agreements and discrepancies are discussed, along with preliminary uncertainty estimate for SAmes. The SAmes provides a good constraint to prevent substantial errors in intensity predictions (e.g. for weak bands and minor isotopologues) and can be further improved. Ames-296K and NOSL-296 may complement each other to provide improved input for future database updates, combining the strengths of EH/EDM and BTRHE approaches. Data available at and https://doi.org/10.48667/9kmk-0334. [ABSTRACT FROM AUTHOR]

It is well known that the convergence of correlation energies in atomic and molecular calculations is relatively slow and that calculations aimed at high accuracy must explicitly make corrections for this. In this work we consider 1e − basis set extrapolation as a means of obtaining high accuracy. The correlation consistent basis sets of Dunning et al. have provided a convenient platform for extrapolation, with the independent variable being X = D, T, Q, 5, … . There has been much debate in the literature about the functional form to use for the extrapolation, with contention between the ‘theoretically justified’ (X + 1)−3 form and empirical forms based on exponentials or variable powers. We will dissect the theoretical justification of the (X + 1)−3 form by considering MP2 calculations on He and Ne as a function of the maximum angular momentum (⪙) in the basis using basis sets having converged radial extent. Calculations with ⪙ up to 14 were carried out for Ne. It is shown that while the asymptotic form of (⪙ + 1)−3 is clearly reached, higher order terms are very important in the range of ⪙ normally used in molecular calculations. We also use similar analysis techniques for an open shell atom and a small molecule. The functional form for the dependence of molecular properties with ⪙ is complex and it is safer to extrapolate fitting parameters than energies. [ABSTRACT FROM AUTHOR]

Using a new method, exponential parameters are developed to add to the Dunning type correlation consistent basis sets to describe core-valence correlation. Compared with existing core-valence basis sets, the new basis sets are larger, but have vastly improved convergence characteristics, especially for low-lying electronic states. The new method is very general in that it allows the explicit inclusion of electronic excited states as well as ionic states in the basis set determination. [ABSTRACT FROM AUTHOR]