Geometry optimizations with the coupled-cluster model CC2 using the resolution-of-the-identity approximation
Geometry optimizations with the coupled-cluster model CC2 using the resolution-of-the-identity approximation
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DOI：
10.1063/1.1564061
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发表时间：
2003-05-01
影响因子：
4.4
通讯作者：
Hättig, C
中科院分区：
文献类型：
--
作者：
Hättig, C
本文报道了二阶耦合团簇单双模型CC 2的梯度的一种实现方法，它采用了对电子排斥积分的分辨恒等式（RI）近似。CC 2模型的基态平衡几何形状和谐波频率的性能进行了研究，并与实验和其他从头算方法进行了比较。结果表明，CC 2平衡几何与Moller-Plesset微扰理论（MP2）计算的结果具有相似的精度，但键长较大.特别地，双键和三键以及富电子化合物中的键被拉长0.5-1.5 μ π ι。因此，对于单键，特别是在富电子化合物中，CC 2略微优于MP2，但是对于强双键和三键，CC 2稍微劣于MP2。谐波频率的结果与平衡结构的结果并行。由RI近似引入的误差被发现是可以忽略不计的剩余的单电子基组的错误相比，如果使用优化的辅助基组。通常，键长的RI误差为10（-3）μ m的量级，角度的误差为10（-3）-10（-2）度。应用程序的几何反式偶氮苯和顺式，反式-1，4-二氟丁二烯的几何形状和谐波频率的报告。(C)2003年，美国物理学会。
An implementation of the gradient for the second-order coupled-cluster singles-and-doubles model CC2 is reported, which employs the resolution-of-the-identity (RI) approximation for electron repulsion integrals. The performance of the CC2 model for ground state equilibrium geometries and harmonic frequencies is investigated and compared with experiment and other ab initio methods. It is found that CC2 equilibrium geometries have a similar accuracy to those calculated with second-order Moller-Plesset perturbation theory (MP2), but the bond lengths are larger. In particular, double and triple bonds and bonds in electron-rich compounds are elongated by 0.5-1.5 pm. Thereby CC2 slightly outperforms MP2 for single bonds, in particular in electron-rich compounds, but for strong double and triple bonds CC2 is somewhat inferior to MP2. The results for harmonic frequencies go in parallel with the results for equilibrium structures. The error introduced by the RI approximation is found to be negligible compared to the remaining one-electron basis set error, if optimized auxiliary basis sets are used. Typically, the RI error in bond lengths is of the order of 10(-3) pm and the error in angles 10(-3)-10(-2) deg. Applications are reported for the geometry of trans-azobenzene and for the geometry and harmonic frequencies of cis,trans-1,4-difluorobutadiene. (C) 2003 American Institute of Physics.