CC2 excitation energy calculations on large molecules using the resolution of the identity approximation
CC2 excitation energy calculations on large molecules using the resolution of the identity approximation
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DOI：
10.1063/1.1290013
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发表时间：
2000-10-01
影响因子：
4.4
通讯作者：
Weigend, F
中科院分区：
文献类型：
--
作者：
Hättig, C;Weigend, F
本文报道了一种适用于大规模积分-直接计算的近似耦合团簇单双法CC2的新实现。它利用双电子积分的恒等式(RI)近似的分辨率来减少计算所需的CPU时间和这些积分的I/O。我们使用CC2方程的分割形式，它消除了存储双激发团簇幅度的需要。与RI近似相结合，CC2方程的这种表述导致了存储器和磁盘空间需求的减少，与先前实现中的O(n(2)N(2))相比，相关电子(N)和基函数(N)的数目分别为O(N-2)和O(NN(2))。减少的CPU、内存和磁盘空间要求使在大分子上使用精确的基组进行CC2计算成为可能，这是传统的CC2方法无法实现的。我们给出了当n=1-12时C2nH_2n+2的垂直激发能的一个应用，并报道了TZVPP基组的最低允许偶极跃迁的结果，当n=12时，它包含1108个基函数。结果表明，对于CC2基态能量和价态激发能，如果采用MP2能量优化的辅助基组，与通常的基组误差相比，RI近似引起的误差可以忽略不计。(C)2000年美国物理研究所。[S0021-9606(00)31237-5]。
A new implementation of the approximate coupled cluster singles and doubles method CC2 is reported, which is suitable for large scale integral-direct calculations. It employs the resolution of the identity (RI) approximation for two-electron integrals to reduce the CPU time needed for calculation and I/O of these integrals. We use a partitioned form of the CC2 equations which eliminates the need to store double excitation cluster amplitudes. In combination with the RI approximation this formulation of the CC2 equations leads to a reduced scaling of memory and disk space requirements with the number of correlated electrons (n) and basis functions (N) to, respectively, O(N-2) and O(nN(2)), compared to O(n(2)N(2)) in previous implementations. The reduced CPU, memory and disk space requirements make it possible to perform CC2 calculations with accurate basis sets on large molecules, which would not be accessible with conventional implementations of the CC2 method. We present an application to vertical excitation energies of alkenes C2nH2n+2, for n=1-12, and report results for the lowest lying dipole-allowed transitions for the TZVPP basis sets, which for n=12 contain 1108 basis functions. Comparison with conventional CC2 results for the smaller alkenes show that for CC2 ground state energies and for excitation energies of valence states, the error due to the RI approximation is negligible compared to the usual basis set error, if auxiliary basis sets are used, which have been optimized for MP2 energy calculations. (C) 2000 American Institute of Physics. [S0021-9606(00)31237-5].