In an attempt to improve on our earlier W3 theory [J. Chem. Phys. {\bf 120}, 4129 (2004)] we consider such refinements as more accurate estimates for the contribution of connected quadruple excitations ($\hat{T}_4$), inclusion of connected quintuple excitations ($\hat{T}_5$), diagonal Born-Oppenheimer corrections (DBOC), and improved basis set extrapolation procedures. Revised experimental data for validation purposes were obtained from the latest version of the ATcT (Active Thermochemical Tables) Thermochemical Network. We found that the CCSDTQ$-$CCSDT(Q) difference converges quite rapidly with the basis set, and that the formula 1.10[CCSDT(Q)/cc-pVTZ+CCSDTQ/cc-pVDZ$-$CCSDT(Q)/cc-pVDZ] offers a very reliable as well as fairly cost-effective estimate of the basis set limit $\hat{T}_4$ contribution. The largest $\hat{T}_5$ contribution found in the present work is on the order of 0.5 kcal/mol (for ozone). DBOC corrections are significant at the 0.1 kcal/mol level in hydride systems. . Based on the accumulated experience, a new computational thermochemistry protocol for first-and second-row main-group systems, to be known as W4 theory, is proposed. Our W4 atomization energies for a number of key species are in excellent agreement (better than 0.1 kcal/mol on average, 95% confidence intervals narrower than 1 kJ/mol) with the latest experimental data obtained from Active Thermochemical Tables. A simple {\em a priori} estimate for the importance of post-CCSD(T) correlation contributions (and hence a pessimistic estimate for the error in a W2-type calculation) is proposed.
Benchmark thermochemistry of the C_nH_{2n+2} alkane isomers (n=2--8) and performance of DFT and composite ab initio methods for dispersion-driven isomeric equilibria
本文用W_4、W_3.2lite和W_1h理论重新研究了八碳以下直链和支链烷烃的热化学。通过等键和次同键反应获得了"准W4"原子化能。我们在0 K时的最佳原子化能量（kcal/mol）为：1220.04正丁烷，1497.01正戊烷，1774.15正己烷，2051.17正庚烷，2328.30正辛烷，1221.73异丁烷，1498.27异戊烷，1501.01新戊烷，1775.22异己烷，1774.61 3-甲基戊烷，1775.67二异丙基、1777.27新己烷、2052.43异庚烷、2054.41新庚烷、2330.67异辛烷和2330.81六甲基乙烷。我们对$ΔH^\circ_{f,298K}$的最佳估计为：-30.00正丁烷、-34.84正戊烷、-39.84正己烷、-44.74正庚烷、-49.71正辛烷、-32.01异丁烷、-36.49异戊烷、-39.69新戊烷、-41.42异己烷、-40.72 3-甲基戊烷、-42.08二异丙基、-43.77新己烷，-46.43异庚烷、-48.84新庚烷、-53.29异辛烷和-53.68六甲基乙烷。这些是在极好的协议（通常优于1 kJ/mol），在298 K的实验生成热从CCCBDB和/或NIST化学网络图书数据库。然而，在0 K的理论和实验（1.1千卡/摩尔）之间的一个很大的差异观察到只有新戊烷。这种偏差主要是由于在计算0 K CCCBDB值时使…
Basis set convergence and extrapolation of connected triple excitation contributions (T) in computational thermochemistry: the W4-17 benchmark with up to k functions
Systematically Improvable Tensor Hypercontraction: Interpolative Separable Density-Fitting for Molecules Applied to Exact Exchange, Second- and Third-Order Møller-Plesset Perturbation Theory
提出了一种基于插值可分密度拟合的张量超压缩（THC）分解方法。我们说明算法的细节，以实现这一目标的框架内，贝克的原子为中心的正交网格。单个ISDF参数$c_\text{ISDF}$控制精度和成本之间的权衡。具体地，$c_\text{ISDF}$设置在THC中使用的内插点的数量，$N_\text{IP} = c_\text{ISDF}\times N_\text{X}$，其中$N_\text{X}$是辅助基函数的数量。结合身份解析（RI）技术，我们开发并研究了用于Hartree-Fock和范围分离混合体（例如，$ω$ B 97 X-V）和四次标度二阶和三阶Møller-Plesset理论（MP2和MP3）。这些算法在W 4 -11热化学（原子化能）集和A24非共价相互作用基准集与标准Dunning基组（cc-pVDZ、cc-pVTZ、aug-cc-pVDZ和aug-cc-pVTZ）上进行了评价。我们证明了收敛的THC-RI算法的数值精确RI结果使用ISDF点。在此基础上，我们对每个基组和方法的$c_\text{ISDF}$提出了建议。我们还演示了THC-RI精确交换和MP2对于水团簇和$\text{C}_{20}$等大型系统的实用性。我们强调，更多的挑战等待在获得准确的和数值稳定的THC分解波函数振幅，以及在大基组的虚拟轨道所跨越的空间，并实现稀疏意识的THC-RI算法。
