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首页> 外文期刊>The Journal of Chemical Physics >Approximating correlation effects in multiconfigurational self-consistent field calculations of spin-spin coupling constants
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Approximating correlation effects in multiconfigurational self-consistent field calculations of spin-spin coupling constants

机译：自旋-自旋耦合常数的多组态自洽场计算中的近似相关效应

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The multiconfigurational self-consistent field (MCSCF) method in their approximations restricted and complete active spaces (RAS and CAS) provides. a theoretically accurate description of the coupling constants of a wide range of molecules. To obtain accurate results, however, very large basis sets and large configuration spaces must be used. Nuclear magnetic resonance coupling constants for the equilibrium geometry have been calculated for a series of small molecules using approximated correlation contributions. The four contributions to the coupling constants (Fermi contact, spin dipolar, orbital paramagnetic, and orbital diamagnetic) have been calculated at the CAS and RAS MCSCF and second-order polarization propagator approximation levels using a large basis set. An additive model that considers the effect on the coupling constants from excitation of more than two electrons. and from core-electron correlation is used to estimate the coupling constants. Compared with the experimental couplings, the best calculated values, which correspond to the MCSCF results, present a mean absolute error of 3.6 Hz and a maximum absolute deviation of 13.4 Hz. A detailed analysis of the different contributions and of the effects of the additive contributions on the coupling constants is carried out. (c) 2008 American Institute of Physics.
机译：多配置自洽字段（MCSCF）方法以其逼近和完全活动空间（RAS和CAS）提供。对各种分子的偶联常数进行理论上准确的描述。但是，为了获得准确的结果，必须使用非常大的基集和很大的配置空间。已经使用近似的相关贡献为一系列小分子计算出了平衡几何的核磁共振耦合常数。耦合常数的四个贡献（费米接触，自旋偶极子，轨道顺磁和轨道抗磁）已在CAS和RAS MCSCF以及二阶极化传播器近似水平下使用较大的基础集进行了计算。考虑了两个以上电子激发对耦合常数的影响的加性模型。并根据核电子相关性估算耦合常数。与实验耦合相比，与MCSCF结果相对应的最佳计算值呈现出3.6 Hz的平均绝对误差和13.4 Hz的最大绝对偏差。对不同的贡献以及加性贡献对耦合常数的影响进行了详细的分析。 （c）2008年美国物理研究所。

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