Evangelista Francesco A
Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA.
J Chem Phys. 2014 Aug 7;141(5):054109. doi: 10.1063/1.4890660.
Applications of the similarity renormalization group (SRG) approach [F. Wegner, Ann. Phys. 506, 77 (1994) and S. D. Głazek and K. G. Wilson, Phys. Rev. D 49, 4214 (1994)] to the formulation of useful many-body theories of electron correlation are considered. In addition to presenting a production-level implementation of the SRG based on a single-reference formalism, a novel integral version of the SRG is reported, in which the flow of the Hamiltonian is driven by a source operator. It is shown that this driven SRG (DSRG) produces a Hamiltonian flow that is analogous to that of the SRG. Compared to the SRG, which requires propagating a set of ordinary differential equations, the DSRG is computationally advantageous since it consists of a set of polynomial equations. The equilibrium distances, harmonic vibrational frequencies, and vibrational anharmonicities of a series of diatomic molecules computed with the SRG and DSRG approximated with one- and two-body normal ordered operators are in good agreement with benchmark values from coupled cluster with singles, doubles, and perturbative triples. Particularly surprising results are found when the SRG and DSRG methods are applied to C2 and F2. In the former case, both methods fail to converge, while in the latter case an unbound potential energy curve is obtained. A modified commutator approximation is shown to correct these problems in the case of the DSRG method.
考虑了相似重整化群（SRG）方法[F. Wegner，《物理学年鉴》506, 77 (1994)以及S. D. Głazek和K. G. Wilson，《物理评论D》49, 4214 (1994)]在构建有用的电子关联多体理论方面的应用。除了基于单参考形式给出SRG的生产级实现之外，还报告了一种新颖的SRG积分形式，其中哈密顿量的流由一个源算子驱动。结果表明，这种驱动SRG（DSRG）产生的哈密顿量流与SRG的类似。与需要传播一组常微分方程的SRG相比，DSRG在计算上具有优势，因为它由一组多项式方程组成。用SRG和DSRG并以一体和二体正规序算子近似计算的一系列双原子分子的平衡距离、简谐振动频率和振动非简谐性与耦合簇单双激发及微扰三重激发的基准值吻合良好。当将SRG和DSRG方法应用于C₂和F₂时，发现了特别令人惊讶的结果。在前一种情况下，两种方法都无法收敛，而在后一种情况下得到了一条非束缚的势能曲线。结果表明，在DSRG方法中，一种修正的对易子近似可以纠正这些问题。
