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【6h】Coupled-cluster methods for open-shell molecular and other many-fermion systems.

机译开壳分子和其他许多费米子体系的耦合簇方法。

【摘要】The description of the electronic structure of radicals and other open-shell molecular systems represents a significant challenge for current theoretical methodologies. Since the low-lying electronic states of open-shell species often possess a manifestly multi-determinantal character, it is difficult to perform calculations for these systems that are both highly accurate and practical enough to be applied to a wide range of chemical problems of interest. To overcome these difficulties, we have developed two new classes of coupled-cluster (CC) methods, which are capable of accounting for the high-level electron correlation effects that characterize open-shell systems at a relatively low computational cost. The first class of methods, the active-space variants of the electron-attached (EA) and ionized (IP) equation-of-motion CC (EOMCC) theories, utilize the idea of applying a linear electron-attaching or ionizing operator to the correlated, ground-state CC wave function of an N -electron closed-shell system in order to generate the ground and excited states of the related (N +/- 1)-electron radical species. Furthermore, these approaches use a physically motivated set of active orbitals to a priori select the dominant higher-order correlation effects to be included in the calculation, which significantly reduces the costs of the high-level approximations needed for obtaining accurate results for open-shell species without sacrificing accuracy. The second class consists of the size extensive, left-eigenstate completely-renormalized (CR) CC approaches based on the biorthogonal formulation of the method of moments of CC equations, in which noniterative corrections due to higher-order excitations are added to the energies obtained with the standard CC approximations, such as CCSD (CC with singles and doubles). We have extended one of the best methods in this category, termed CR-CC(2,3) or CR-EOMCC(2,3), in which a noniterative correction due to triple excitations is added to the CCSD or EOMCCSD energy, and its higher-order CR-CC(2,4)/CR-EOMCC(2,4) approach, in which a noniterative correction due to triple and quadruple excitations is added to the CCSD/EOMCCSD energy, to open-shell systems. In this thesis the theoretical details of all of these new methodologies as well as a sample of benchmark examples that illustrate their performance in studies of ground and excited states of open-shell molecular systems are discussed. In addition, since there is nothing in the underlying theoretical framework specific to electronic structure, the CC approaches developed in this thesis are not restricted to molecular cases and can be applied to other many- fermion systems, such as atomic nuclei. Representative examples of applications of the new CC methods developed in this thesis research in the context of quantum chemistry to studies of nuclear structure are given as well.

【摘要机译】自由基和其他开壳分子系统的电子结构的描述对当前的理论方法提出了重大挑战。由于开壳物种的低洼电子态通常具有明显的多决定性特征,因此很难对这些系统进行足够精确且实用的计算,以应用于广泛的感兴趣的化学问题。为了克服这些困难,我们开发了两类新的耦合簇(CC)方法,它们能够以相对较低的计算成本解决表征开壳系统的高级电子相关效应。第一类方法是电子附着(EA)和离子化(IP)运动CC(EOMCC)理论的有效空间变体,它采用了将线性电子附着或电离算子应用于电子N电子闭壳系统的相关基态CC波函数,以生成相关(N +/- 1)电子自由基基团的基态和激发态。此外,这些方法使用一组物理激励的主动轨道来先验选择要包括在计算中的主要高阶相关效应,从而显着降低了获得精确的开壳结果所需的高层近似的成本种而不牺牲准确性。第二类包括基于CC方程矩法的双正交公式的,尺寸扩展的,左本征态完全重归一化(CR)CC方法,其中将高阶激励引起的非迭代校正添加到获得的能量中标准CC近似值,例如CCSD(带有单打和双打的CC)。我们扩展了这一类别中的最佳方法之一,称为CR-CC(2,3)或CR-EOMCC(2,3),其中,由于三次激励而引起的非迭代校正被添加到CCSD或EOMCCSD能量中,并且其高阶CR-CC(2,4)/ CR-EOMCC(2,4)方法,其中将由于三重和四重激发而产生的非迭代校正添加到CCSD / EOMCCSD能量中,用于开壳系统。在本文中,我们讨论了所有这些新方法的理论细节,并举例说明了基准实例的示例,这些实例说明了它们在开壳分子系统的基态和激发态研究中的性能。此外,由于在基本理论框架中没有电子结构特有的内容,因此本文开发的CC方法并不局限于分子情况,而是可以应用于其他许多费米子体系,例如原子核。并给出了在量子化学的背景下,本文研究开发的新型CC方法在核结构研究中的应用实例。

【作者】Gour, Jeffrey R.;

【作者单位】Michigan State University.;

【年(卷),期】2010(),

【年度】2010

【页码】192 p.

【总页数】192

【原文格式】PDF

【正文语种】eng

【中图分类】;

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