Importance of the consideration of anharmonic motion in charge-density studies: a comparison of variable-temperature studies on two explosives, RDX and HMX

Multipole models of the electron density in a hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) crystal were obtained at 20, 120 and 298 K followed by topological analysis. The necessity of anharmonic model refinements for RDX is demonstrated, and the results are compared with refinements for 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX). The reliability of anisotropic atomic displacement parameters for H atoms is discussed.