Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Okazaki, Aichi, 444-8585, Japan.
Phys Chem Chem Phys. 2012 Jun 7;14(21):7809-20. doi: 10.1039/c2cp23767a. Epub 2012 May 10.
The canonical transformation (CT) theory has been developed as a multireference electronic structure method to compute high-level dynamic correlation on top of a large active space reference treated with the ab initio density matrix renormalization group method. This article describes a parallelized algorithm and implementation of the CT theory to handle large computational demands of the CT calculation, which has the same scaling as the coupled cluster singles and doubles theory. To stabilize the iterative solution of the CT method, a modification to the CT amplitude equation is introduced with the inclusion of a level shift parameter. The level-shifted condition has been found to effectively remove a type of intruder state that arises in the linear equations of CT and to address the discontinuity problems in the potential energy curves observed in the previous CT studies.
典范变换（CT）理论已被开发为一种多参考电子结构方法，用于在使用从头算密度矩阵重整化群方法处理的大活性空间参考上计算高阶动态相关。本文描述了一种并行化算法和 CT 理论的实现，以处理 CT 计算的大规模计算需求，其与耦合簇单双激发理论的规模相同。为了稳定 CT 方法的迭代解，引入了对 CT 振幅方程的修改，其中包括能级移动参数。已发现能级移动条件可有效地消除 CT 线性方程中出现的一种闯入态，并解决之前 CT 研究中观察到的势能曲线不连续性问题。
