Owen Andrew N, Sahoo Nitai P, Esselman Brian J, Stanton John F, Woods R Claude, McMahon Robert J
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Quantum Theory Project, Departments of Physics and Chemistry, University of Florida, Gainesville, Florida 32611, USA.
J Chem Phys. 2022 Jul 21;157(3):034303. doi: 10.1063/5.0101064.
Hydrazoic acid (HN) is used as a case study for investigating the accuracy and precision by which a molecular structure-specifically, a semi-experimental equilibrium structure (r )-may be determined using current state-of-the-art methodology. The influence of the theoretical corrections for effects of vibration-rotation coupling and electron-mass distribution that are employed in the analysis is explored in detail. The small size of HN allowed us to deploy considerable computational resources to probe the basis-set dependence of these corrections using a series of coupled-cluster single, double, perturbative triple [CCSD(T)] calculations with cc-pCVXZ (X = D, T, Q, 5) basis sets. We extrapolated the resulting corrections to the complete basis set (CBS) limit to obtain CCSD(T)/CBS corrections, which were used in a subsequent r structure determination. The r parameters obtained using the CCSD(T)/cc-pCV5Z corrections are nearly identical to those obtained using the CCSD(T)/CBS corrections, with uncertainties in the bond distances and angles of less than 0.0006 Å and 0.08°, respectively. The previously obtained r structure using CCSD(T)/ANO2 agrees with that using CCSD(T)/cc-pCV5Z to within 0.000 08 Å and 0.016° for bond distances and angles, respectively, and with only 25% larger uncertainties, validating the idea that r structure determinations can be carried out with significantly smaller basis sets than those needed for similarly accurate, strictly ab initio determinations. Although the purely computational r structural parameters [CCSD(T)/cc-pCV6Z] fall outside of the statistical uncertainties (2σ) of the corresponding r structural parameters, the discrepancy is rectified by applying corrections to address the theoretical limitations of the CCSD(T)/cc-pCV6Z geometry with respect to basis set, electron correlation, relativity, and the Born-Oppenheimer approximation, thereby supporting the contention that the semi-experimental approach is both an accurate and vastly more efficient method for structure determinations than is brute-force computation.
叠氮酸（HN）被用作一个案例研究，以考察使用当前最先进的方法确定分子结构（具体而言，是半实验平衡结构(r)）的准确性和精确性。详细探讨了分析中所采用的振动 - 转动耦合和电子质量分布效应的理论校正的影响。HN分子的小尺寸使我们能够投入大量计算资源，使用一系列具有cc - pCVXZ（X = D、T、Q、5）基组的耦合簇单双微扰三重态[CCSD(T)]计算来探究这些校正对基组的依赖性。我们将所得校正外推到完整基组（CBS）极限，以获得CCSD(T)/CBS校正，并将其用于后续的(r)结构确定。使用CCSD(T)/cc - pCV5Z校正获得的(r)参数与使用CCSD(T)/CBS校正获得的参数几乎相同，键长和键角的不确定性分别小于0.0006 Å和0.08°。先前使用CCSD(T)/ANO2获得的(r)结构与使用CCSD(T)/cc - pCV5Z获得的结构在键长和键角方面分别在0.00008 Å和0.016°以内相符，且不确定性仅大25%，这验证了一个观点，即与同样精确的严格从头算确定所需的基组相比，可以使用明显更小的基组来进行(r)结构确定。尽管纯计算得到的(r)结构参数[CCSD(T)/cc - pCV6Z]超出了相应(r)结构参数的统计不确定性（2σ），但通过应用校正来解决CCSD(T)/cc - pCV6Z几何结构在基组、电子相关性、相对论性和玻恩 - 奥本海默近似方面的理论局限性，这种差异得以纠正，从而支持了这样一种观点，即半实验方法对于结构确定而言是一种比蛮力计算既准确又高效得多的方法。
