论文标题
轨道空间中的多级CC2和CCSD：大分子系统中的电子激发
Multilevel CC2 and CCSD in reduced orbital spaces: electronic excitations in large molecular systems
论文作者
论文摘要
我们介绍了多级CC2（MLCC2）和多级CCSD（MLCCSD）模型的有效实现。随着系统尺寸的增加，MLCC2和MLCCSD展示了较低级耦合群集模型的缩放。为了治疗大型系统，我们将MLCC2和MLCCSD与降低的轨道空间方法相结合，其中多级耦合群集计算以显着截断的分子轨道基础进行。截断方案基于分子系统的活性区域的选择以及随后的局部哈特里孔轨道的构造。这些轨道用于多级耦合群集计算中。电子排斥积分是使用筛选方案进行巧妙分解的，该方案可以保证在截短的分子轨道基础上进行准确性。 Cholesky因素是直接在截短的基础上构建的，从而确保了较低的存储要求。甚至可以使用多级Hartree-fock参考来处理较大的系统。通过减少空间方法，我们可以处理具有超过一千个原子的系统。这是水溶液中偏氨二氨氨酸的证明。
We present efficient implementations of the multilevel CC2 (MLCC2) and multilevel CCSD (MLCCSD) models. As the system size increases, MLCC2 and MLCCSD exhibit the scaling of the lower level coupled cluster model. In order to treat large systems, we combine MLCC2 and MLCCSD with a reduced orbital space approach where the multilevel coupled cluster calculation is performed in a significantly truncated molecular orbital basis. The truncation scheme is based on the selection of an active region of the molecular system and the subsequent construction of localized Hartree-Fock orbitals. These orbitals are used in the multilevel coupled cluster calculation. The electron repulsion integrals are Cholesky decomposed using a screening protocol that guarantees accuracy in the truncated molecular orbital basis. The Cholesky factors are constructed directly in the truncated basis, ensuring low storage requirements. Even larger systems can be treated by using a multilevel Hartree-Fock reference. With the reduced space approach, we can handle systems with more than a thousand atoms. This is demonstrated for paranitroaniline in aqueous solution.
