In the context of high-accuracy computational thermochemistry, the valence CCSD correlation component of molecular atomization energies present the most severe basis set convergence problem, followed by the (T) component. In the present paper, we make a detailed comparison, for an expanded version of the W4-11 thermochemistry benchmark, between on the one hand orbital-based CCSD/AV{5,6}Z+d and CCSD/ACV{5,6}Z extrapolation, and on the other hand CCSD-F12b calculations with cc-pVQZ-F12 and cc-pV5Z-F12 basis sets. This latter basis set, now available for H--He, B--Ne, and Al--Ar, is shown to be very close to the basis set limit. Apparent differences (which can reach 0.35 kcal/mol for systems like CCl4) between orbital-based and CCSD-F12b basis set limits disappear if basis sets with additional radial flexibility, such as ACV{5,6}Z, are used for the orbital calculation. Counterpoise calculations reveal that, while TAEs with V5Z-F12 basis sets are nearly free of BSSE, orbital calculations have significant BSSE even with AV(6+d)Z basis sets, leading to non-negligible differences between raw and counterpoise-corrected extrapolated limits. This latter problem is greatly reduced by switching to ACV{5,6}Z core-valence basis sets, or simply adding an additional zeta to just the valence orbitals. Previous reports that all-electron approaches like HEAT lead to different CCSD(T) limits than valence limit+CV correction approaches like FPD and W4 theory can be rationalized in terms of the greater radial flexibility of core-valence basis sets. W4-F12 is found to agree slightly better than W4 with ATcT (active thermochemical tables) data, at a substantial saving in CPU time and especially I/O overhead. A W4-F12 calculation on benzene is presented as a proof of concept.
The Hydration Structure of Carbon Monoxide by Ab Initio Methods
一氧化碳（CO）在液态水中的溶剂化作用对于理解其毒理学效应和生物化学作用具有重要意义。本文采用从头算分子动力学（AIMD）和CCSD（T）-F12计算方法，对Straub和Karplus分子力学（MM）模型计算CO（aq）的准确性进行了评估。CCSD（T）-F_（12）CO-H_2 O势能面表明，最稳定的结构对应于与C中心提供氢键的水。MM计算的表面错误地预测O原子是比C原子更强的氢键受体。AIMD模拟表明，CO像疏水溶质一样被溶剂化，与水的氢键非常有限。MM模型倾向于高估氢键的程度和高估C原子的原子半径。水化吉布斯自由能的计算值与实验值（9.3 kJ/mol calc. vs 10.7 kJ/mol实验）。CO（aq）在TIP 3 P模型水中的计算扩散系数为5.19 × 10-5 cm 2/s（计算值），是实验值2.32 x 10-5 cm 2/s的两倍以上
Ab Initio Characterization of C2H4N2 Isomers: Structures, electronic energies, spectroscopic parameters and formation pathways
Universidad Autónoma de Chile（智利自治大学）；Universidad de Chile（智利大学）；Università di Bologna（博洛尼亚大学）；Universidad de Huelva（韦尔瓦大学）；CSIC-UHU（西班牙国家研究委员会-韦尔瓦大学联合单位）；Instituto de Estructura de la Materia, IEM-CSIC（物质结构研究所，IEM-CSIC）
Single-electron Fluorine Bonding. I. The SEFB-15 and CSFB-14 Benchmark Datasets, Reference Binding Energies and Intermolecular Bond Distances: Assessment of M06-2X density functional
Inorganic and Physical Chemistry, Indian Institute of Science（印度科学研究所无机与物理化学）
我们报道了开壳层双原子分子氧化钇（YO）光谱的从头算研究。该研究考虑了六个最低的双重态，$X\,{}^{2}Σ^{+}$，$A\,{}^{2}Π$，$C\,{}^{2}Π$，$A'\,{}^{2}Δ$，$B\,{}^{2}Σ^{+}$，$D\,{}^{2}Σ^{+}$和一些更高的躺四重态使用高水平的电子结构理论和精确的核运动计算。采用耦合团簇单重、双重和微扰三重、CCSD（T）和多参考组态相互作用（MRCI）方法，结合钇原子上的相对论赝势和一系列相关一致的基组，基组的大小从三重$ζ$到五重$ζ$。考虑了核价相关效应，对CCSD（T）进行了完整的基组极限外推。自旋轨道耦合是通过使用MRCI状态相互作用与自旋轨道（SI-SO）方法和四分量相对论运动方程CCSD计算。利用从头算数据，计算了6条势能曲线，12条自旋轨道曲线，8条电子角动量曲线，6条电偶极矩曲线和12条跃迁偶极矩曲线（4条平行，8条垂直），完整地描述了6个最低双态的光谱. Duo核运动程序用于求解这六个电子态的耦合核运动薛定谔方程。不同温度下模拟的$^{89}$ Y $^{16}$ O的光谱与几个可用的高分辨率实验研究进行了比较，发现一旦微小的调整，电子激发能的良好协议。
Preparing Small Gaussian Basis for Highly Accurate Ab Initio Description of Lithium Rydberg States
FZU - Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Institute of Physics, Faculty of Mathematics and Physics, Charles University（查尔斯大学数学物理学院物理研究所）
A fully {\it ab initio} potential curve of near-spectroscopic quality for the OH^- anion: importance of connected quadruple excitations and scalar relativistic effects
对羟基阴离子OH ^{-}的基态电势曲线进行了基准研究，包括1粒子和n粒子基组的详细校准。CCSD（T）基组极限高估了$ω_e$约10 cm ^{-1}，这只能通过在耦合团簇展开中包含连接的四重激发--或者等效地，在多参考计算的有效空间中包含$2π$轨道来补救。在包含标量相对论效应（$ω_e$上的~3 cm ^{-1}）后，获得光谱质量（亚cm ^{-1}精度）的势曲线。我们最好的计算EA（OH），1.828 eV，同意小数点后三位的最佳实验值。我们计算的最佳离解能D_0（OH ^-）= 4.7796 eV和D_0（OH）= 4.4124 eV表明实验D_0（OH）= 4.392 eV可能偏低了0.02 eV。
Nuclear moments, charge radii, and magnetization distribution parameters of Ag isotopes from laser spectroscopy and \textit{ab initio} electronic-structure calculations
Petersburg Nuclear Physics Institute named by B.P. Konstantinov of National Research Centre “Kurchatov Institute”（以B.P.康斯坦丁诺夫命名的国家研究中心“库尔恰托夫研究所”圣彼得堡核物理研究所）；Saint Petersburg State University（圣彼得堡国立大学）；KU Leuven, Instituut voor Kern- en Stralingsfysica（荷语鲁汶大学核与辐射物理研究所）；Centre for Cold Matter, Imperial College London（伦敦帝国理工学院冷物质中心）；State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University（清华大学物理系低维量子物理国家重点实验室）
