Efficient and accurate local single reference correlation methods for high-spin open-shell molecules using pair natural orbitals
Efficient and accurate local single reference correlation methods for high-spin open-shell molecules using pair natural orbitals
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DOI：
10.1063/1.3663855
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发表时间：
2011-12-07
影响因子：
4.4
通讯作者：
Neese, Frank
中科院分区：
文献类型：
--
作者：
Hansen, Andreas;Liakos, Dimitrios G.;Neese, Frank
本文报道了在局域对自然轨道（LPNO）概念框架下，高自旋开壳层（自旋不受限制）单参考耦合对、二次组态相互作用和耦合团簇方法的生产级实现。这项工作是早期开发的闭壳层LPNO方法的扩展[F。尼塞，F. Wennmohs和A.汉森，化学物理杂志130，114108（2009）; F.尼塞，A.汉森和D. G. Liakos，J.Chem.Phys.131，064103（2009）]。内部空间由定域轨道跨越，而每个电子对的外部空间由截断的PNO展开表示。与大量PNO相关联的费力的积分变换通过密度拟合（身份解析（RI））技术的广泛使用而变得可行。所产生的开壳层的情况下，使用准限制轨道的参考行列式的建设技术的并发症进行了详细讨论。在闭壳层情况下，只有三个截止参数控制每个电子对的PNO的平均数量，有效对列表的大小，以及每个PNO的辅助基函数的数量。所选择的阈值默认值确保了鲁棒性，并且父规范方法的结果以高精度再现。对绝对和相对能量以及时间的全面数值测试一致表明，LPNO方法的出色性能可以通过微小的修改延续到开壳层情况。最后，超精细耦合计算变分LPNO-CEPA/1方法，其中存在一个定义良好的期望值类型的密度，表明了巨大的潜力的LPNO方法的有效计算的分子性质。(C)2011年美国物理学会。[doi：10.1063/1.3663855]
A production level implementation of the high-spin open-shell (spin unrestricted) single reference coupled pair, quadratic configuration interaction and coupled cluster methods with up to doubly excited determinants in the framework of the local pair natural orbital (LPNO) concept is reported. This work is an extension of the closed-shell LPNO methods developed earlier [F. Neese, F. Wennmohs, and A. Hansen, J. Chem. Phys. 130, 114108 (2009); F. Neese, A. Hansen, and D. G. Liakos, J. Chem. Phys. 131, 064103 (2009)]. The internal space is spanned by localized orbitals, while the external space for each electron pair is represented by a truncated PNO expansion. The laborious integral transformation associated with the large number of PNOs becomes feasible through the extensive use of density fitting (resolution of the identity (RI)) techniques. Technical complications arising for the open-shell case and the use of quasi-restricted orbitals for the construction of the reference determinant are discussed in detail. As in the closed-shell case, only three cutoff parameters control the average number of PNOs per electron pair, the size of the significant pair list, and the number of contributing auxiliary basis functions per PNO. The chosen threshold default values ensure robustness and the results of the parent canonical methods are reproduced to high accuracy. Comprehensive numerical tests on absolute and relative energies as well as timings consistently show that the outstanding performance of the LPNO methods carries over to the open-shell case with minor modifications. Finally, hyperfine couplings calculated with the variational LPNO-CEPA/1 method, for which a well-defined expectation value type density exists, indicate the great potential of the LPNO approach for the efficient calculation of molecular properties. (C) 2011 American Institute of Physics. [doi:10.1063/1.3663855]