A new near-linear scaling, efficient and accurate, open-shell domain-based local pair natural orbital coupled cluster singles and doubles theory.
A new near-linear scaling, efficient and accurate, open-shell domain-based local pair natural orbital coupled cluster singles and doubles theory.
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DOI：
10.1063/1.4981521
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发表时间：
2017-04
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影响因子：
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通讯作者：
Masaaki Saitow;Ute Becker;Christoph Riplinger;Edward F. Valeev;F. Neese
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文献类型：
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作者：
Masaaki Saitow;Ute Becker;Christoph Riplinger;Edward F. Valeev;F. Neese
耦合团簇展开，截断后的单和双激发（CCSD），提供了准确和可靠的分子电子波函数和能量的许多分子系统周围的平衡几何形状。然而，高计算成本，这是众所周知的规模为O（N6）与系统大小N，限制了它的实际应用，由不超过约20-30个原子组成的小系统。为了克服这些局限性，在过去的几年中，低阶尺度近似CCSD已被深入研究。在我们以前的工作中，我们已经表明，通过结合对自然轨道（PNO）方法和轨道域的概念，可以实现完全线性缩放的CC实现（DLPNO-CCSD和DLPNO-CCSD（T）），恢复约99.9%的总相关能量[C. Riplinger等人，J. Chem.Phys.144，024109（2016）]。DLPNO-CCSD和DLPNO-CCSD（T）方法的生产级实现被证明适用于由相对适中的硬件上的常规黑盒方式的几百个原子组成的现实系统。2011年，提出了一种用于高自旋开壳层非限制性Hartree-Fock参考波函数的减标度CCSD方法（UHF-LPNO-CCSD）[A.汉森等人，J. Chem.Phys.135，214102（2011）]。经过几年的经验，这种方法，一些缺点UHF-LPNO-CCSD注意到，需要重新设计的方法，这是本文的主题。为此，我们采用高自旋开壳层的N-电子价微扰理论形式主义的变体来定义初始猜测波函数，因此也开壳层PNO。由于所有的截断和近似都严格类似于闭壳情况，因此新的PNO近似正确地收敛到闭壳极限。此外，考虑到形式主义使用单组轨道的事实，仅需要单个PNO积分变换，这提供了大量的计算节省。我们发现，与默认的PNO截断参数，约99.9%的总CCSD相关能量回收开壳层物种，这是可比的性能的方法为闭壳层。UHF-DLPNO-CCSD在闭壳层系统中表现出线性标度行为，而在开壳层系统中则表现出线性到二次标度行为。我们考虑过的最大的系统包含超过500个原子，并且具有超过10000个具有三重质量基组的基函数。
The Coupled-Cluster expansion, truncated after single and double excitations (CCSD), provides accurate and reliable molecular electronic wave functions and energies for many molecular systems around their equilibrium geometries. However, the high computational cost, which is well-known to scale as O(N6) with system size N, has limited its practical application to small systems consisting of not more than approximately 20-30 atoms. To overcome these limitations, low-order scaling approximations to CCSD have been intensively investigated over the past few years. In our previous work, we have shown that by combining the pair natural orbital (PNO) approach and the concept of orbital domains it is possible to achieve fully linear scaling CC implementations (DLPNO-CCSD and DLPNO-CCSD(T)) that recover around 99.9% of the total correlation energy [C. Riplinger et al., J. Chem. Phys. 144, 024109 (2016)]. The production level implementations of the DLPNO-CCSD and DLPNO-CCSD(T) methods were shown to be applicable to realistic systems composed of a few hundred atoms in a routine, black-box fashion on relatively modest hardware. In 2011, a reduced-scaling CCSD approach for high-spin open-shell unrestricted Hartree-Fock reference wave functions was proposed (UHF-LPNO-CCSD) [A. Hansen et al., J. Chem. Phys. 135, 214102 (2011)]. After a few years of experience with this method, a few shortcomings of UHF-LPNO-CCSD were noticed that required a redesign of the method, which is the subject of this paper. To this end, we employ the high-spin open-shell variant of the N-electron valence perturbation theory formalism to define the initial guess wave function, and consequently also the open-shell PNOs. The new PNO ansatz properly converges to the closed-shell limit since all truncations and approximations have been made in strict analogy to the closed-shell case. Furthermore, given the fact that the formalism uses a single set of orbitals, only a single PNO integral transformation is necessary, which offers large computational savings. We show that, with the default PNO truncation parameters, approximately 99.9% of the total CCSD correlation energy is recovered for open-shell species, which is comparable to the performance of the method for closed-shells. UHF-DLPNO-CCSD shows a linear scaling behavior for closed-shell systems, while linear to quadratic scaling is obtained for open-shell systems. The largest systems we have considered contain more than 500 atoms and feature more than 10 000 basis functions with a triple-ζ quality basis set.