Density functional calculations of the hyperpolarisabilities of small molecules

Density functional calculations of the static first hyperpolarisability are reported for several small molecules using: (1) generalised gradient approximation (GGA) functionals, (2) asymptotically corrected GGA functionals, (3) hybrid functionals. The calculations are compared with similar studies of van Gisbergen, Snijders and Baerends (J. Chem. Phys. 109 (1998) 10657) (GSB). We conclude that the asymptotic behaviour is a crucially important aspect, with good results being obtained using the HCTH(AC) functional, which are of similar quality to those of GSB using the LB94 functional. However, we conclude that the most reliable approach for the calculation of hyperpolarisabilities using DFT is to use one of the latest hybrid functionals, such as B97-1. The additional flexibility of this functional and its improved asymptotic behaviour are responsible for this conclusion.