Electron correlations, benzene dimer

Effects of the higher electron correlation correction on the calculated intermolecular interaction energies of benzene and naphthalene dimers comparison between MP2 and CCSD(T) calculations ... 

Calculation of Intermolecular Interactions in the Benzene Dimer Using Coupled-Cluster and Local Electron Correlation Methods. 

Recently reported systematic calculations for small molecular clusters show that CCSD(T) calculations using very large basis sets provide accurate inter-molecular interaction energies [6,7]. The CCSD(T)-level electron correlation correction is highly computationally demanding. The CPU time for a CCSD(T) calculation is proportional to the seventh power of the number of basis functions. In early calculations, the MP2 method was used for the evaluation of the interactions of aromatic molecules. The CPU time for an MP2 calculation is proportional to the fifth power of the munber of basis functions. However, recently reported CCSD(T) calculations of the benzene dimer show that the MP2 method overestimates the attraction considerably compared with the more reliable CCSD(T) calculations [9,11]. A comparison of HP, MP2 and CCSD(T) calculations for the benzene dimer is shown in Fig. 3. The MP2 calculation substantially overestimates the attraction com-... 

Fig. 3 Effect of electron correlation on the benzene dimer interaction energy...

Subsequently, applications were made to larger systems such as the ethyne and benzene dimers (Hesselmann et al. 2005 Podeszwa and Szalewicz 2005) where, once again, the accuracy of the method was demonstrated. More recently, the DFT-SAPT implementation has been used to study the interaction of water on graphene (Jenness and Jordan 2009), DNA base pairs (Hesselmann et al. 2006), and DNA base pair tetramers (Fiethen et al. 2008). Calculations of such accuracy are simply not possible using conventional electronic structure methods in the supermolecular approach, particularly as the only correlated ab initio method with a reasonable computational scaling is MP2, and MP2 is not suitable for the interactions of systems with 7T-bonding (Sinnokrot et al. 2002). 

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