Computational protocol for modeling thermochromic molecular crystals: Salicylidene aniline as a case study

A computational protocol that combines periodic and QM/QM' calculations has been applied to investigate the structural (geometrical and electronic) and photophysical absorption properties of the salicylidene aniline (SA) thermochromic molecular crystal. The protocol consists of three different steps, namely (i) the description of the molecular crystal using a periodic approach taking into account dispersion interactions, (ii) the identification of reliable finite models (clusters), and (iii) the calculation of vertical transition energies including environmental effects through the use of an electronic embedding model (QM/QM' ONIOM approach). The encouraging results obtained in this work for the β polymorph of SA, both in terms of accuracy and computational cost, open the way to the simulation and the prediction of the photophysical behavior of other molecular crystals, especially those much less well characterized experimentally.