A third-order multireference perturbation theory based on the driven similarity renormalization group approach (DSRG-MRPT3) is presented. The DSRG-MRPT3 method has several appealing features: a) it is intruder free, b) it is size consistent, c) it leads to a non-iterative algorithm with ${\cal O}(N^6)$ scaling, and d) it includes reference relaxation effects. The DSRG-MRPT3 scheme is benchmarked on the potential energy curves of F$_2$, H$_2$O$_2$, C$_2$H$_6$, and N$_2$ along the F-F, O-O, C-C, and N-N bond dissociation coordinates, respectively. The nonparallelism errors of DSRG-MRPT3 are consistent to those of CASPT3 and MRCISD, and show significant improvements over those obtained from DSRG second-order multireference perturbation theory. Our efficient implementation of the DSRG-MRPT3 based on factorized electron repulsion integrals enables studies of medium-sized open-shell organic compounds. This point is demonstrated with computations of the singlet-triplet splitting ($Δ_{\rm ST} = E_{\rm T} - E_{\rm S}$) of 9,10-anthracyne. At the DSRG-MRPT3 level of theory, our best estimate of the adiabatic $Δ_{\rm ST}$ is 3.9 kcal mol$^{-1}$, a value that is within 0.1 kcal mol$^{-1}$ from multireference coupled cluster results.
Improving the efficiency of the multireference driven similarity renormalization group via sequential transformation, density fitting, and the non-interacting virtual orbital approximation
Spin-free formulation of the multireference driven similarity renormalization group: A benchmark study of first-row diatomic molecules and spin-crossover energetics
Analytical Gradient Theory for Spin-Free State-Averaged Second-Order Driven Similarity Renormalization Group Perturbation Theory (SA-DSRG-MRPT2) and Its Applications for Conical Intersection Optimizations
A driven similarity renormalization group approach to quantum many-body problems
相似重整化群（SRG）方法的应用[F. Wegner，Ann.Phys.506，77（1994），S. D. Gadhazek和K. G. Wilson，Phys.Rev.D49，4214（1994）]对建立有用的电子关联多体理论的重要作用。除了提出一个生产级实现的SRG的基础上的单参考形式主义，一个新的积分版本的SRG的报告，其中的流动的哈密顿是由一个源操作。结果表明，这种驱动SRG（DSRG）产生的哈密顿流是类似的SRG。与需要传播一组常微分方程的SRG相比，DSRG在计算上是有利的，因为它由一组多项式方程组成。用一体和二体正规有序算符近似的SRG和DSRG计算了一系列双原子分子的平衡距离、谐波振动频率和振动非谐性，与单重、双重和微扰三重耦合团簇的基准值[CCSD（T）]吻合得很好.当SRG和DSRG方法应用于C $_2$和F $_2$时，发现了特别令人惊讶的结果。在前一种情况下，两种方法都不能收敛，而在后一种情况下，得到的是一条未结合的势能曲线。一个修改的换向器近似示出的DSRG方法的情况下，以纠正这些问题。
Renormalization group approach to second-order Green's function theory
University of Münster（明斯特大学）；Center for Multiscale Theory and Computation, University of Münster（明斯特大学多尺度理论与计算中心）；University of Hamburg（汉堡大学）；The Hamburg Centre for Ultrafast Imaging (CUI)（汉堡超快成像中心）
