论文标题
评估相对论相关的电子结构计算中的MP2冷冻天然轨道
Assessing MP2 frozen natural orbitals in relativistic correlated electronic structure calculations
论文作者
论文摘要
具有相关电子数量和基集的大小的高计算缩放是一种瓶颈，该瓶颈限制了耦合群集（CC）算法的应用。对于基于2个或4种组件相对论的哈密顿量的计算，这尤其是这样，该计算通常采用未合同的基集并导致较大的虚拟分子轨道（VMO）空间。与规范Hartree-fock（HF）相比，使用更紧凑的虚拟纺纱器可以通过使用更紧凑的虚拟旋转器来缓解此问题，例如基于天然轨道（NOS）的旋转器。在本文中，我们描述了用于为相关波形生成NOS的实现，尤其是MP2冷冻的天然轨道（MP2FNOS），这是我们新颖的相对论耦合聚类理论实施的组成部分[J. J. Pototschnig等。 Al。，J。Chem。理论计算。 17、5509、2021]。我们的实施能够操纵复合物和四个元素密度矩阵，从而可以生成Kramers限制性和Kramers无限制的MP2FNOS。此外，NOS在父原子轨道（AO）的基础上重新表达，因此该代码还可以在AO的基础上生成CCSD天然轨道以进行进一步分析。通过研究CCSD水平的相关能量和分子特性的MP2FNOS的截断误差，例如Nuclei（EFGS）的电场梯度，电偶极子和四极矩的氢矩，用于Hyder hx（x = f-ts）和Parity-violation-violation-violation-violation-vioLation-vioLating y $ ___2 $ ___2 MP2FNO在元素周期表上以大致均匀的方式加速了相关能量的收敛性，并且随着VMO空间的截断，其截断为全部空间尺寸的一半左右，因此可以获得对两个能量的可靠估计值，并考虑了所有分子特性。
The high computational scaling with the number of correlated electrons and the size of the basis set is a bottleneck which limits applications of coupled cluster (CC) algorithms. This is particularly so for calculations based on 2- or 4-component relativistic Hamiltonians, which often employ uncontracted basis sets and lead to large virtual molecular orbital (VMO) spaces. This problem may be alleviated by employing a more compact set of virtual spinors than those provided by the canonical Hartree-Fock (HF) set, such as those based on natural orbitals (NOs). In this paper we describe the implementation of a module for generating NOs for correlated wavefunctions, and in particular MP2 frozen natural orbitals (MP2FNOs), as a component of our novel implementation of relativistic coupled cluster theory for massively parallel architectures [J. Pototschnig et. al., J. Chem. Theory Comput. 17, 5509, 2021]. Our implementation is capable of manipulating both complex and quaternion density matrices, thus allowing for the generation of both Kramers-restricted and Kramers-unrestricted MP2FNOs. Furthermore, NOs are re-expressed in the parent atomic orbital (AO) basis, so that the code also makes it possible to generate CCSD natural orbitals in AO basis for further analysis. By investigating the truncation errors of MP2FNOs for both the correlation energy and molecular properties at CCSD level such as the electric field gradients at the nuclei (EFGs), electric dipole and quadrupole moments for hydrogen halides HX (X=F-Ts), and parity-violating energy differences (PV) for H$_2$Y$_2$ (Y=O-Se), we find that MP2FNOs accelerate the convergence of the correlation energy in a roughly uniform manner across the periodic table and that, with VMO spaces truncated to around half the size of the full spaces ones, it is possible to obtain reliable estimates for both energies and all molecular properties considered.
