We have accurately estimated the dipole moment (mu), the static linear polarizability (alpha) over bar and first hyperpolarizability (beta(tot) and beta(HRS)) per unit of long linear chains of HCN and HNC molecules, using the MP2/6-311++G(2d,2p) approach. It is found for both isomers that the intermolecular interactions have a substantial impact on the first hyperpolarizability, in comparison with the corresponding monomer results. For the infinite HCN [HNC] chains, the extrapolated values for mu, (alpha) over bar, beta(tot) and beta(HRS) per unit are estimated in 1.655 [2.145], 16.96 [19.42], 76.6 [134.9] and 32.4 [54.6] a.u., respectively. (C) 2013 Elsevier B.V. All rights reserved.