Elongation method and supermolecule approach for the calculation of nonlinear susceptibilities. Application to the 3-Methyl-4-Nitropyridine 1-Oxide and 2-Methyl-4-Nitroaniline crystals. - Feng Long Gu; Maxime Guillaume; Edith Botek; Benoît Champagne 002; Frédéric Castet; Laurent Ducasse; Yuriko Aoki (J. Comput. Methods Sci. Eng., 2006)