The physical models for materials response under external perturbations constitute the foundation of different scientific fields, as the materials engineering or solid state physics. However, in many cases, it is not easy to establish a direct relation between the parameters of the model and the material components. Therefore, the implementation of practical applications for the laboratory and the homework will enhance the learning experience. In order to do this, we have developed a virtual laboratory for materials engineering using free software, the web-based interface WEBMO and the computational chemistry package MOPAC2007. In this communication we explain our experience for a practical case, the materials refractive index. We detail the task, main results and conclusions in the study of this property and a discussion of the possible use of this practical case as a tool for Problem Based Learning.