We present a possible approach for the computation of free energies and ensemble averages of one-dimensional coarse-grained models in materials science. The approach is based upon a thermodynamic limit process, and makes use of ergodic theorems and large deviations theory. In addition to providing a possible efficient computational strategy for ensemble averages, the approach allows for assessing the accuracy of approximations commonly used in practice. This is joint work with X. Blanc (University Paris 6), F. Legoll (ENPC-INRIA) and C. Patz (Weierstrass-Institut, Berlin), submitted to journal of nonlinear science, preprint available at http://hal.inria.fr/inria-00282107/en/.