Hyperpolarizabilities of molecular chains: A real-space approach

First principles calculations can provide important insight into the mechanisms of non-linear molecular response. Chain molecules are of particular interest due to their large and directional response, but calculating their non-linear response coefficients is a computational challenge. We have developed a real-space approach to evaluate the linear polarizability and first and second hyperpolarizability of molecular chains within Kohn-Sham density functional theory. Different approaches to minimize uncertainties in particular in the second hyperpolarizability γ are presented. We tested our scheme by calculating the response of model hydrogen chains using local and non-local density functionals. Differences between explicit density functionals and orbital functionals are discussed.