Nonempirical density-functional theory for van der Waals interactions

In previous work, Kannemann and Becke [ J. Chem. Theory Comput. 5, 719 (2009) and J. Chem. Theory Comput. 6, 1081 (2010) ] have demonstrated that the generalized gradient approximations (GGAs) of Perdew and Wang for exchange [Phys. Rev. B 33, 8800 (1986)] and Perdew, Burke, and Ernzerhof for correlation [Phys. Rev. Lett. 77, 3865 (1996)] , plus the dispersion density functional of Becke and Johnson [J. Chem. Phys. 127, 154108 (2007)] , comprise a nonempirical density-functional theory of high accuracy for thermochemistry and van der Waals complexes. The theory is nonempirical except for two universal cutoff parameters in the dispersion energy. Our calculations so far have been grid-based and have employed the local density approximation (LDA) for the orbitals. In this work, we employ orbitals from self-consistent GGA calculations using Gaussian basis sets. The results, on a benchmark set of 65 van der Waals complexes, are similar to our grid-based post-LDA results. This work sets the stage for van der Waals force computations and geometry optimizations.