Department of Chemistry and Cherry Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA.
J Chem Phys. 2017 Mar 28;146(12):124132. doi: 10.1063/1.4979016.
A third-order multireference perturbation theory based on the driven similarity renormalization group (DSRG-MRPT3) approach 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 O(N) scaling, and (d) it includes reference relaxation effects. The DSRG-MRPT3 scheme is benchmarked on the potential energy curves of F, HO, CH, and N along the F-F, O-O, C-C, and N-N bond dissociation coordinates, respectively. The nonparallelism errors of DSRG-MRPT3 are consistent with those of complete active space third-order perturbation theory and multireference configuration interaction with singles and doubles 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=E-E) of 9,10-anthracyne. At the DSRG-MRPT3 level of theory, our best estimate of the adiabatic Δ is 3.9 kcal mol, a value that is within 0.1 kcal mol from multireference coupled cluster results.
提出了一种基于驱动相似重整化群（DSRG-MRPT3）方法的三阶多参考微扰理论。DSRG-MRPT3 方法具有几个吸引人的特点：（a）它没有侵入者，（b）它是大小一致的，（c）它导致具有 O（N）标度的非迭代算法，（d）它包括参考松弛效应。DSRG-MRPT3 方案在 F、HO、CH 和 N 的势能曲线基准上进行了测试，分别沿 F-F、O-O、C-C 和 N-N 键离解坐标。DSRG-MRPT3 的非平行误差与完全活性空间三阶微扰理论和单双激发多参考组态相互作用的误差一致，并显示出相对于 DSRG 二阶多参考微扰理论的显著改进。我们基于因式化电子排斥积分的 DSRG-MRPT3 的有效实现使中等大小的开壳有机化合物的研究成为可能。这一点通过对 9,10-蒽的单重态-三重态分裂（Δ=E-E）的计算得到了证明。在 DSRG-MRPT3 理论水平上，我们对绝热Δ的最佳估计值为 3.9 kcal mol，与多参考耦合簇结果相差 0.1 kcal mol。
