Unrestricted Coupled Cluster and Brueckner Doubles Variations of W1 Theory
Unrestricted Coupled Cluster and Brueckner Doubles Variations of W1 Theory
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DOI：
10.1021/ct900260g
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发表时间：
2009-10-01
影响因子：
5.5
通讯作者：
Martin, Jan M. L.
中科院分区：
文献类型：
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作者：
Barnes, Ericka C.;Petersson, George A.;Martin, Jan M. L.
Weizmann-1 理论 (W1) 的无限制耦合簇自旋污染校正 [UCCSD(T)] 和无限制 Brueckner 双态 [UBD(T)] 变体（分别表示为 W1U、W1Usc 和 W1BD）与受限制的开壳层 W1 理论 [W1(RO)] 进行比较。四个 W1 变体的性能在 G2/97 测试集中使用 220 个总原子化能、电子亲和力、电离势和质子亲和力进行评估，以与原始 W1 (RO) 研究的误差分析保持一致。 W1U (0.65 +/- 0.48 kcal/mol)、W1Usc (0.57 +/- 0.48 kcal/mol)、W1BD (0.62 +/- 0.48 kcal/mol) 和 W1(RO) (0.57 +/- 10.48 kcal/mol) 实验的均方根偏差表明这四种方法实际上无法区分。该误差分析排除了“单态双根”、C-2 和 O-3，因为单行列式方法对于这些强多参考系统来说并不真正足够。对于这种高度自旋污染和多参考物种，不受限制的 W1 变体表现不佳（对于 O-3 EA，W1Usc 与实验的最大偏差为 -4.2 +/- 0.1 kcal/mol）。对于这些病理情况，W1(RO) 的表现比其不受限制的对应物要好得多（O-3 EA 的实验偏差减少到 -1.5 +/- 0.1 kcal/mol），尽管误差明显大于整个测试集的误差。 C-2、O-3 和 F-2 势能曲线的示例表明，使用 W1BD 的优点是 <S-e> 中的误差与能量误差的大小相关，而 W1 (RO) 在没有此类警告的情况下会失去准确性。
Unrestricted coupled cluster spin contamination corrected [UCCSD(T)] and unrestricted Brueckner doubles [UBD(T)] variations of the Weizmann-1 theory (W1), denoted as W1U, W1Usc, and W1BD, respectively, are compared with the restricted open-shell W1 theory [W1(RO)]. The performances of the four W1 variants are assessed with 220 total atomization energies, electron affinities, ionization potentials, and proton affinities in the G2/97 test set, for consistency with the error analysis of the original W1 (RO) study. The root-mean-square deviations from the experiment of W1U (0.65 +/- 0.48 kcal/mol), W1Usc (0.57 +/- 0.48 kcal/mol), W1BD (0.62 +/- 0.48 kcal/mol), and W1(RO) (0.57 +/- 10.48 kcal/mol) show that the four methods are virtually indistinguishable. This error analysis excludes the "singlet biradicals," C-2 and O-3, since single determinantal methods are not really adequate for these strongly multireference systems. The unrestricted W1 variants perform poorly for such highly spin-contaminated and multireference species (the largest deviation from experiment for W1Usc is -4.2 +/- 0.1 kcal/mol for the O-3 EA). W1(RO) performs much better than its unrestricted counterparts for these pathological cases (the deviation from experiment is reduced to -1.5 +/- 0.1 kcal/mol for the O-3 EA), though the errors are significantly larger than those for the overall test set. The examples Of C-2, O-3, and the F-2 potential energy curve indicate that an advantage to using W1BD is that the error in < S-e > correlates with the magnitude of the error in energy, whereas W1 (RO) loses accuracy without such a warning.