Ab initio and DFT studies for accurate description of van der Waals interaction between He atoms

To evaluate the accuracy of density functional theory (DFT) for describing van der Waals interaction, we performed CCSD(T), MP4(SDTQ) and several DFT calculations for the He dimer. The results clarified that (1) CCSD(T) and M P4(SDTQ) with an 'adjusted' diffuse basis-set reproduce the experimental bi nding energy as well as the equilibrium distance, (2) MP3 and MP2 underesti mate the binding energy, (3) B3LYP and B3PW91 completely fail to describe t he binding, (4) Perdew-Wang exchange-correlation functional and its modifie d ones can provide a He-He binding state, although the calculated binding e nergies are largely overestimated. The basis-set dependence of the binding energy was also discussed. (C) 2001 Elsevier Science B.V. All rights reserv ed.