Naphthalene dimer, CCSD

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 ... 

The MP2 method was mainly used for ab initio calculations of the naphthalene dimer. Very recently CCSD(T) interaction energies of a few naphthalene dimers were estimated. The conclusions derived from the calculations are as follows (1) the naphthalene dimer has two nearly isoenergetic stable structures (shpped-parallel and cross structures shown in Fig. 7), (2) the sandwich and T-shaped structures are unstable, (3) dispersion is the major source of the attraction, (4) electrostatics stabilizes the T-shaped structure, while dispersion increases the relative stability of the shpped-parallel and cross structures, and (5) the large dispersion energy is the cause of the stabiUty of the slipped-parallel and cross structures. 

CCSD(T) calculations of the naphthalene dimer using a large basis set are extremely difficult therefore, the MP2 method was used even in recently reported calculations [61-63]. The MP2 interaction energy depends significantly on the basis set (- 3.74 to - 10.69 kcal/mol) nevertheless, all the MP2 calculations concluded that the slipped-parallel dimer is stabler than the T-shaped dimer. Local MP2 calculations also show the same preference [64]. Very recently reported CCSD(T) interaction energies of the naphthalene dimers at the basis set limit show that the slipped-parallel and rrn j dimers are the stablest (- 5.28 and - 5.73 kcal/mol, respectively) and the T-shaped and sandwich dimers are substantially less stable (- 4.34 and - 3 78 kcal/mol respectively) [30]. /. ... 

MP2 calculations of the benzene-naphthalene and naphthalene-anthracene complexes show that the shpped-parallel orientation is stabler than the T-shaped one [62,70]. An interesting conclusion was reported from MP2 calculations on a set of aromatic complexes, namely that the energies of the T-shaped and shpped-parallel structures are quite comparable when the molecules are small, but the shpped-parallel structure becomes stabler than the T-shaped one as the molecules become larger [62]. The same conclusion was derived from the CCSD(T) interaction energies for the benzene and naphthalene dimers [9,30]. 

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