Schmitz Gunnar, Hättig Christof
Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44801 Bochum, Germany.
J Chem Phys. 2016 Dec 21;145(23):234107. doi: 10.1063/1.4972001.
We present an implementation of pair natural orbital coupled cluster singles and doubles with perturbative triples, PNO-CCSD(T), which avoids the quasi-canonical triples approximation (T0) where couplings due to off-diagonal Fock matrix elements are neglected. A numerical Laplace transformation of the canonical expression for the perturbative (T) triples correction is used to avoid an I/O and storage bottleneck for the triples amplitudes. Results for a test set of reaction energies show that only very few Laplace grid points are needed to obtain converged energy differences and that PNO-CCSD(T) is a more robust approximation than PNO-CCSD(T0) with a reduced mean absolute deviation from canonical CCSD(T) results. We combine the PNO-based (T) triples correction with the explicitly correlated PNO-CCSD(F12*) method and investigate the use of specialized F12-PNOs in the conventional triples correction. We find that no significant additional errors are introduced and that PNO-CCSD(F12*)(T) can be applied in a black box manner.
我们展示了一种带有微扰三重激发的配对自然轨道耦合簇单双激发方法（PNO-CCSD(T)）的实现，该方法避免了准正则三重激发近似（T0），在T0中忽略了非对角Fock矩阵元引起的耦合。对微扰（T）三重激发校正的正则表达式进行数值拉普拉斯变换，以避免三重激发振幅出现输入/输出和存储瓶颈。一组反应能量测试结果表明，只需极少的拉普拉斯网格点就能获得收敛的能量差，并且与PNO-CCSD(T0)相比，PNO-CCSD(T)是一种更稳健的近似方法，其与正则CCSD(T)结果的平均绝对偏差更小。我们将基于PNO的（T）三重激发校正与显式相关的PNO-CCSD(F12*)方法相结合，并研究在传统三重激发校正中使用专门的F12-PNO。我们发现不会引入显著的额外误差，并且PNO-CCSD(F12*)(T)可以以黑箱方式应用。
