Levine Benjamin G, Durden Andrew S, Esch Michael P, Liang Fangchun, Shu Yinan
Institute for Advanced Computational Science and Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA.
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Chem Phys. 2021 Mar 7;154(9):090902. doi: 10.1063/5.0042147.
The complete active space self-consistent field (CASSCF) method has seen broad adoption due to its ability to describe the electronic structure of both the ground and excited states of molecules over a broader swath of the potential energy surface than is possible with the simpler Hartree-Fock approximation. However, it also has a reputation for being unwieldy, computationally costly, and un-black-box. Here, we discuss a class of alternatives, complete active space configuration interaction (CASCI) methods, paying particular attention to their application to electronic excited states. The goal of this Perspective is fourfold. First, we argue that CASCI is not merely an approximation to CASSCF, in that it can be designed to have important qualitative advantages over CASSCF. Second, we present several insights drawn from our experience experimenting with different schemes for computing orbitals to be employed in CASCI. Third, we argue that CASCI is well suited for application to nanomaterials. Finally, we reason that, with the rise in new low-scaling approaches for describing multireference systems, there is a greater need than ever to develop new methods for defining orbitals that provide an efficient and accurate description of both static correlation and electronic excitations in a limited active space.
完全活性空间自洽场（CASSCF）方法因其能够在比简单的Hartree-Fock近似更宽的势能面上描述分子基态和激发态的电子结构而得到广泛应用。然而，它也因难以处理、计算成本高且不具备黑箱性质而闻名。在此，我们讨论一类替代方法，即完全活性空间组态相互作用（CASCI）方法，特别关注它们在电子激发态方面的应用。本综述的目标有四个。首先，我们认为CASCI不仅仅是CASSCF的一种近似，因为它可以被设计成具有比CASSCF更重要的定性优势。其次，我们展示了从我们对用于CASCI的不同轨道计算方案进行实验的经验中得出的一些见解。第三，我们认为CASCI非常适合应用于纳米材料。最后，我们推断，随着用于描述多参考系统的新的低标度方法的兴起，比以往任何时候都更需要开发新的轨道定义方法，以便在有限的活性空间中对静态关联和电子激发提供高效且准确的描述。
