Evaluation of electrostatic descriptors for predicting crystalline density

This study evaluates the importance of electrostatic corrections to earlier quantum-mechanically based methods to predict crystal densities of neutral and ionic molecular energetic materials. Our previous methods (B. M. Rice et al., J. Phys. Chem. A 2007, 111, 10874) use the molecular volumes of the isolated molecule or formula unit to estimate the crystal density; this volume is defined to be that inside the quantum-mechanically determined 0.001 a.u. isosurface of electron density surrounding the isolated molecule. The electrostatic corrections to these volumetric estimates are based on features of the electrostatic potential mapped onto this isosurface of electron density, and have been parameterized using information from 180 neutral and 23 ionic CHNO molecular systems. The quality of the electrostatically corrected methods was assessed through application to 38 neutral and 48 ionic compounds not used in the parameterization. The root mean square (rms) percent deviation and average absolute error of predictions for the 38 neutral species relative to experiment are 2.7% and 0.035 g/cm(3), respectively, decreases of 0.9% and 0.015 g/cm(3) from the earlier predictions (3.6% and 0.050 g/cm(3), respectively). The rms percent deviation and average absolute error of predictions for the 48 ionic compounds relative to experiment are 3.7% and 0.045 g/cm(3), respectively, decreases of 2.6% and 0.043 g/cm(3) from the earlier predictions that used the formula unit volumes only. The results clearly show a significant improvement to the earlier method upon inclusion of electrostatic corrections.