Frozen Virtual Natural Orbitals for Coupled-Cluster Linear-Response Theory.
Frozen Virtual Natural Orbitals for Coupled-Cluster Linear-Response Theory.
复制标题
耦合簇线性响应理论的冻结虚拟自然轨道。
DOI：
10.1021/acs.jpca.6b11410
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
T. Crawford
中科院分区：
文献类型：
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作者：
Ashutosh Kumar;T. Crawford
冻结虚拟自然轨道（NO）的方法，其中未占用的轨道空间是使用相关的密度，如从多体微扰理论，已被证明产生紧凑的波函数，用于确定基态相关能量和相关的属性，与相应的占用数提供了一个指导虚拟空间的截断。在这项工作中，这种方法是第一次测试的高阶响应特性的计算，特别是频率依赖的偶极极化率使用耦合簇理论。我们发现，这样的属性是更敏感的截断虚拟空间在NO的基础上比在原来的正则分子轨道（CMO）的基础上，与截断误差线性增加的冻结虚拟NO的数量。这种表现不佳的原因包括更分散的性质，NO的低占领数，以及减少稀疏的扰动单振幅在NO的基础和忽视的轨道响应。我们测试了一些方法来提高NO空间的性能，包括使用场扰动密度来定义虚轨道和各种外部空间校正。另一方面，截断的CMO空间，产生的误差小于2%的耦合团偶极极化率，即使在删除多达50%的整个虚拟空间。我们发现，这种积极的表现的CMO空间的结果从取消的错误，由于截断的未扰动和扰动的振幅，以及稀疏的单打振幅。我们引入了一个称为偶极振幅的简单标准，用作截断此类属性计算的CMO基础的阈值。
The frozen-virtual natural-orbital (NO) approach, whereby the unoccupied-orbital space is constructed using a correlated density such as that from many-body perturbation theory, has proven to yield compact wave functions for determining ground-state correlation energies and associated properties, with corresponding occupation numbers providing a guide to the truncation of the virtual space. In this work this approach is tested for the first time for the calculation of higher-order response properties, particularly frequency-dependent dipole polarizabilities using coupled-cluster theory. We find that such properties are much more sensitive to the truncation of virtual space in the NO basis than in the original canonical molecular orbital (CMO) basis, with truncation errors increasing linearly with respect to the number of frozen virtual NOs. The reasons behind this poor performance include the more diffuse nature of NOs with low occupation numbers as well as the reduction in sparsity of the perturbed singles amplitudes in the NO basis and the neglect of orbital response. We tested a number of approaches to improve the performance of the NO space, including the use of a field-perturbed density to define the virtual orbitals and various external-space corrections. The truncation of the CMO space, on the other hand, yields errors in coupled-cluster dipole polarizabilities of less than 2% even after removing as much as 50% of the full virtual space. We find that this positive performance of the CMO space results from a cancellation of errors due to the truncation of the unperturbed and perturbed amplitudes, as well as sparsity of the singles amplitudes. We introduce a simple criterion called a dipole amplitude to use as a threshold for truncating the CMO basis for such property calculations.