A RELATIONSHIP BETWEEN THE IMPACT SENSITIVITY AND THE ELECTRONIC-STRUCTURES FOR THE UNIQUE N-N BOND IN THE HMX POLYMORPHS

Ab initio self-consistent field (the 4-31G level) and second-order Mol ler-Plesset perturbation calculations (the MP2/4-31G level) have been carried out on the electronic and the molecular structure of the HMX p olymorphs (alpha, beta, gamma, delta) in crystal. It is found that the re is an intimate relationship between the impact sensitivity (beta << alpha less-than-or-equal-to gamma < delta) and total energy (beta < a lpha < gamma < delta). Furthermore, in order to investigate the quantu m chemical characteristics of the N-N bond in connection with impact s ensitivity in HMX polymorphs (alpha, beta, gamma, delta), an N-N bindi ng potential curve (the MP2/4-31G level) was plotted as a function of the N-N bond length. In order to characterize potential energy curve a s a function of the N-N bond length, a new parameter deltaD (the cryst al effect parameter) was defined as the difference between partially o ptimized N-N bond length and the N-N bond length in the crystal. A goo d correlation between the deltaD values of the HMX polymorphs and the impact sensitivity was found. The physicochemical meaning of the delta D value is discussed in connection with the impact sensitivity.