How dependent are molecular and atomic properties on the electronic structure method? Comparison of Hartree‐Fock,DFT, and MP2 on a biologically relevant set of molecules

This article compares molecular properties and atomic properties defined by the quantum theory of atoms in molecules (QTAIM) obtained from three underlying levels of theory: MP2(full), density functional theory (DFT) (B3LYP), and Hartree‐Fock (H‐F). The same basis set (6‐311++G(d,p)) has been used throughout the study. The calculations and comparisons were applied to a set of 30 small molecules representing common fragments of biological molecules. The molecular properties investigated are the energies and the electrostatic moments (up to and including the quadrupoles), and the atomic properties include electron populations (and atomic charge), atomic dipolar and quadrupolar polarizations, atomic volumes, and corrected and raw atomic energies. The Cartesian distance between dipole vectors and the Frobenius distance between the quadrupole tensors calculated at the three levels of theory provide a measure of their correlation (or lack thereof). With the exception of energies (atomic and molecular), it is found that both DFT and H‐F are in excellent agreement with MP2, especially with regards to the electrostatic mutipoles up to the quadrupoles, but DFT and MP2 agree better in almost all studied properties (with the exception of molecular geometries). QTAIM properties whether obtained from H‐F, DFT(B3LYP), or MP2 calculations when used in the construction of empirical correlations with experiment such as quantitative structure‐activity‐(or property)‐relationships (QSAR/QSPR) are equivalent (because the properties calculated at the three levels are very highly correlated among themselves with r² typically >0.95, and therefore preserving trends). These results suggest that the massive volume of results that were published in the older literature at the H‐F level is valid especially when used to study trends or in QSAR or QSPR studies, and, as long as our test set of molecules is representative, there is no pressing need to re‐evaluate them at other levels of theory except when inadequate basis sets were used by today's standards. Extensive tabulation of molecular and atomic properties at the three theoretical levels is available in the Supporting Information, including optimized geometries, molecular energies, virial ratios, molecular electrostatic moments up to and including hexadecapoles, atomic populations, atomic volumes, atomic electrostatic moments up to and including the quadrupoles, and atomic energies. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

连接性指数及其逆指数对-元醇折光指数的拓扑研究

定义了原子特征值βi和βi＇，由βi建构连接性指数^mXA，由βi＇建构其逆指数^mXB，运用定量结构-性质相关技术研究了42个-元醇分子的折光指数与分子结构间的定量关系。通过多元回归的方法建立了^mXZ和^mXB与折光指数的定量结构性质模型，回归方程为：nD=0．1419^0XA^-1＋0．0434^1XA^-1-0．2534^0XB^-1-0．1460^1XB^-1＋1．4659。对醇折光指数的计算结果表明，预测值与实验值的一致性令人满意，平均相对误差为0．15％。研究表明连接性指数及其逆指数在一起使用可以更好地反映出醇的构效关系。     

New atom-type-based AI topological indices: Application to QSPR studies of aldehydes and ketones

Multiple linear regression (MLR) analysis based on a combined use of the modified Xu index and the atom-type based AI indices is performed to construct quantitative structure-property models on several data sets of organic compounds including aliphatic aldehydes and/or ketones. For each of the physical properties (the normal boiling points, molar refractions, gas heat capacities at 25 degrees C, water solubility at 25 degrees C, and n-octanol/water partition coefficient at 25 degrees C), high quality QSPR models are obtained, particularly the decrease in the standard error is within the range of 23.6-75.9% relative to the linear models with the modified Xu index alone. For individual subsets containing only aldehydes or ketones, in the majority of cases the quality of the model can be further improved. The significant improvement verifies the efficiency of the present approach and also indicates the usefulness of these indices for application to a wide range of physical properties. The results indicate that the physical properties studied are dominated by molecular size but atom types have smaller influences, especially the oxygen atom seems to be most important due to intermolecular polar interactions. The final models are validated to be statistically reliable using the leave-one-out cross-validation and/or an external test set.     

原子配分参数、配分连接性指数及其应用

结构决定性质，性质反映结构，这是化学、生物学等学科的一条基本规律。因此，分子的微观结构与性质之间存在着密切关系。物质的理化性质、生物活性等数据的获取，迄今主要来自于实验。如能建立结构与性能之间的数量关系用以估算与预测分子的性质，这无疑是一项十分有意义的工作。拓扑指数法以其计算简单、准确性高、应用范围广而在上述领域中发挥重要作用犤１～４犦。拓扑指数是对分子结构进行的定量描述，使分子之间的结构差异定量化。自Wiener提出第一个拓扑指数（W）犤５犦以来，迄今已有２００余种拓扑指数问世。其中一部分能够有效地…