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.