一种受限开壳层全基组模型化学方法。
A restricted-open-shell complete-basis-set model chemistry.
作者信息
Wood Geoffrey P F, Radom Leo, Petersson George A, Barnes Ericka C, Frisch Michael J, Montgomery John A
机构信息
School of Chemistry and ARC Centre of Excellence in Free Radical Chemistry and Biotechnology, University of Sydney, Sydney, New South Wales 2006, Australia.
出版信息
J Chem Phys. 2006 Sep 7;125(9):094106. doi: 10.1063/1.2335438.
A restricted-open-shell model chemistry based on the complete basis set-quadratic Becke3 (CBS-QB3) model is formulated and denoted ROCBS-QB3. As the name implies, this method uses spin-restricted wave functions, both for the direct calculations of the various components of the electronic energy and for extrapolating the correlation energy to the complete-basis-set limit. These modifications eliminate the need for empirical corrections that are incorporated in standard CBS-QB3 to compensate for spin contamination when spin-unrestricted wave functions are used. We employ an initial test set of 19 severely spin-contaminated species including doublet radicals and both singlet and triplet biradicals. The mean absolute deviation (MAD) from experiment for the new ROCBS-QB3 model (3.6+/-1.5 kJ mol(-1)) is slightly smaller than that of the standard unrestricted CBS-QB3 version (4.8+/-1.5 kJ mol(-1)) and substantially smaller than the MAD for the unrestricted CBS-QB3 before inclusion of the spin correction (16.1+/-1.5 kJ mol(-1)). However, when applied to calculate the heats of formation at 298 K for the moderately spin-contaminated radicals in the G2/97 test set, ROCBS-QB3 does not perform quite as well as the standard unrestricted CBS-QB3, with a MAD from experiment of 3.8+/-1.6 kJ mol(-1) (compared with 2.9+/-1.6 kJ mol(-1) for standard CBS-QB3). ROCBS-QB3 performs marginally better than standard CBS-QB3 for the G2/97 set of ionization energies with a MAD of 4.1+/-0.1 kJ mol(-1) (compared with 4.4+/-0.1 kJ mol(-1)) and electron affinities with a MAD of 3.9+/-0.2 kJ mol(-1) (compared with 4.3+/-0.2 kJ mol(-1)), but the differences in MAD values are comparable to the experimental uncertainties. Our overall conclusion is that ROCBS-QB3 eliminates the spin correction in standard CBS-QB3 with no loss in accuracy.
基于完备基组二次Becke3（CBS-QB3）模型构建了一种受限开壳层模型化学方法，并将其命名为ROCBS-QB3。顾名思义，该方法使用自旋受限波函数，既用于直接计算电子能量的各个分量，也用于将相关能外推到完备基组极限。这些修改消除了标准CBS-QB3中为补偿使用自旋非受限波函数时的自旋污染而引入的经验校正的必要性。我们使用了一个包含19种严重自旋污染物种的初始测试集，包括双重自由基以及单重态和三重态双自由基。新的ROCBS-QB3模型与实验值的平均绝对偏差（MAD）为（3.6±1.5 kJ mol⁻¹），略小于标准非受限CBS-QB3版本的（4.8±1.5 kJ mol⁻¹），且远小于包含自旋校正之前非受限CBS-QB3的MAD（16.1±1.5 kJ mol⁻¹）。然而，当应用于计算G2/97测试集中中等自旋污染自由基在298 K时的生成热时，ROCBS-QB3的表现不如标准非受限CBS-QB3，与实验值的MAD为3.8±1.6 kJ mol⁻¹（标准CBS-QB3为2.9±1.6 kJ mol⁻¹）。对于G2/97电离能集，ROCBS-QB3的表现略优于标准CBS-QB3，MAD为4.1±0.1 kJ mol⁻¹（标准CBS-QB3为4.4±0.1 kJ mol⁻¹），对于电子亲和能，MAD为3.9±0.2 kJ mol⁻¹（标准CBS-QB3为4.3±0.2 kJ mol⁻¹），但MAD值的差异与实验不确定性相当。我们的总体结论是，ROCBS-QB3消除了标准CBS-QB3中的自旋校正，且精度没有损失。
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