Valeev Edward F, Janssen Curtis L
Center for Computational Molecular Science and Technology, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
J Chem Phys. 2004 Jul 15;121(3):1214-27. doi: 10.1063/1.1759319.
Ab initio electronic structure approaches in which electron correlation explicitly appears have been the subject of much recent interest. Because these methods accelerate the rate of convergence of the energy and properties with respect to the size of the one-particle basis set, they promise to make accuracies of better than 1 kcal/mol computationally feasible for larger chemical systems than can be treated at present with such accuracy. The linear R12 methods of Kutzelnigg and co-workers are currently the most practical means to include explicit electron correlation. However, the application of such methods to systems of chemical interest faces severe challenges, most importantly, the still steep computational cost of such methods. Here we describe an implementation of the second-order Møller-Plesset method with terms linear in the interelectronic distances (MP2-R12) which has a reduced computational cost due to the use of two basis sets. The use of two basis sets in MP2-R12 theory was first investigated recently by Klopper and Samson and is known as the auxiliary basis set (ABS) approach. One of the basis sets is used to describe the orbitals and another, the auxiliary basis set, is used for approximating matrix elements occurring in the exact MP2-R12 theory. We further extend the applicability of the approach by parallelizing all steps of the integral-direct MP2-R12 energy algorithm. We discuss several variants of the MP2-R12 method in the context of parallel execution and demonstrate that our implementation runs efficiently on a variety of distributed memory machines. Results of preliminary applications indicate that the two-basis (ABS) MP2-R12 approach cannot be used safely when small basis sets (such as augmented double- and triple-zeta correlation consistent basis sets) are utilized in the orbital expansion. Our results suggest that basis set reoptimization or further modifications of the explicitly correlated ansatz and/or standard approximations for matrix elements are necessary in order to make the MP2-R12 method sufficiently accurate when small orbital basis sets are used. The computer code is a part of the latest public release of Sandia's Massively Parallel Quantum Chemistry program available under GNU General Public License.
电子相关显式出现的从头算电子结构方法最近备受关注。由于这些方法加快了能量和性质相对于单粒子基组大小的收敛速度，它们有望使对于比目前能以这种精度处理的更大化学体系，实现优于1千卡/摩尔的计算精度成为可能。库策尔尼克及其同事的线性R12方法是目前包含显式电子相关的最实用手段。然而，将此类方法应用于具有化学意义的体系面临严峻挑战，最重要的是，此类方法的计算成本仍然很高。在此，我们描述了一种二阶莫勒 - 普莱塞特方法的实现，其包含电子间距离的线性项（MP2 - R12），由于使用了两个基组，其计算成本有所降低。MP2 - R12理论中使用两个基组的方法最近由克洛珀和萨姆森首次研究，被称为辅助基组（ABS）方法。其中一个基组用于描述轨道，另一个辅助基组用于近似精确MP2 - R12理论中出现的矩阵元。我们通过对积分直接MP2 - R12能量算法的所有步骤进行并行化，进一步扩展了该方法的适用性。我们在并行执行的背景下讨论了MP2 - R12方法的几种变体，并证明我们的实现在各种分布式内存机器上都能高效运行。初步应用结果表明，当在轨道展开中使用小基组（如增强双 - 和三 - ζ相关一致基组）时，双基组（ABS）MP2 - R12方法不能安全使用。我们的结果表明，为了在使用小轨道基组时使MP2 - R12方法足够精确，需要进行基组重新优化或对显式相关假设和/或矩阵元的标准近似进行进一步修改。该计算机代码是桑迪亚大规模并行量子化学程序最新公开版本的一部分，可根据GNU通用公共许可证获取。
