Accuracy of dispersion-corrected DFT calculations of elastic tensors of organic molecular structures

The prediction of elastic tensors of those organic molecular structures in which the intermolecular bonding is mainly due to van der Waals interactions requires "dispersion corrected" DFT calculations in order to ensure that the ground state structure is reasonable. Here we predict the full elastic tensor of triclinic TATB (1,3,5-triamino-2,4,6-trinitrobenzene). We evaluate the accuracy of the prediction by comparison of calculated values with experimentally well constrained elastic tensors for orthorhombic hexogen (RDX, 1,3,5-trinitroperhydro-1,3,5-triazine) and monoclinic tolane, melamine and aspirin. We conclude that the predicted athermal elastic stiffness coefficients are systematically larger than the experimental ambient temperature values by ~20-30% when using the Grimme or Tkatchenko-Scheffler semi-empirical dispersion correction. Both models perform similarly well, but, in comparison to experiment, the anisotropy of longitudinal effects is not fully reproduced by either model.