Yanai Takeshi, Chan Garnet Kin-Lic
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, USA.
J Chem Phys. 2007 Sep 14;127(10):104107. doi: 10.1063/1.2761870.
The canonical transformation theory of Yanai and Chan [J. Chem. Phys. 124, 194106 (2006)] provides a rigorously size-extensive description of dynamical correlation in multireference problems. Here we describe a new formulation of the theory based on the extended normal ordering procedure of Mukherjee and Kutzelnigg [J. Chem. Phys. 107, 432 (1997)]. On studies of the water, nitrogen, and iron oxide potential energy curves, the linearized canonical transformation singles and doubles theory is competitive in accuracy with some of the best multireference methods, such as the multireference averaged coupled pair functional, while computational timings (in the case of the iron oxide molecule) are two to three orders of magnitude faster and comparable to those of the complete active space second-order perturbation theory. The results presented here are greatly improved both in accuracy and in cost over our earlier study as the result of a new numerical algorithm for solving the amplitude equations.
柳井和陈的正则变换理论[《化学物理杂志》124, 194106 (2006)]为多参考问题中的动力学关联提供了一种严格的尺寸可扩展性描述。在此，我们基于穆克吉和库策尔尼希的扩展正规排序程序[《化学物理杂志》107, 432 (1997)]描述了该理论的一种新形式。在对水、氮和氧化铁势能曲线的研究中，线性化正则变换单双激发理论在精度上与一些最佳的多参考方法（如多参考平均耦合对函数）具有竞争力，而计算时间（在氧化铁分子的情况下）快两到三个数量级，并且与完全活性空间二阶微扰理论相当。由于一种求解振幅方程的新数值算法，这里给出的结果在精度和成本方面都比我们早期的研究有了极大的改进。
