Compression behavior of energetic ε‐CL‐20 crystals from density functional theory calculations

Abstract

Using dispersion corrected density functional theory, we comprehensively explore the structure and the Raman spectra of hexanitrohexaazaisowurtzitane (CL‐20) crystal under hydrostatic and uniaxial compression. Through hydrostatic compression, we verify that PBE‐D2 scheme can accurately describe the crystal structure under zero pressure and high pressure. Along different orientation compressions, the CL‐20 crystal exhibits considerable anisotropy in principal stresses and shear stresses. The compression effects on the vibration properties of CL‐20 are further analyzed. Compression along the [100] orientation induces some anomalous changes for vibrational modes of the nitro groups, which are associated with changes of the spatial orientation of the nitro groups. This work is expected to shed light on the anisotropic behavior and pressure‐induced configurations transitions of CL‐20 at atomistic scale.

Collective Variables for Conformational Polymorphism in Molecular Crystals

“…The molecular conformations in the polymorphs differ mainly in the improper angles between the nitro groups and the center cage carbon atoms (see Figure ). Previous computational studies focused on gas- and solid-phase static calculations − or the interaction energy of CL-20 with various materials. − No MD simulations of polymorphic phase transitions between the ambient CL-20 forms have been performed previously. Below, we first present the procedure for identifying CVs to describe conformational polymorphism in molecular crystals.…”

High‐pressure‐induced multiple phase transitions of parabanic acid

“…Raman signals were recorded using a thermoelectrically cooled charge coupled device (CCD, Syncerity, Horiba Jobin Yvon) with a spectral resolution set of 1 cm À1 . First-principles density functional theory [25][26][27][28] calculations of high-pressure crystal structures were performed by the pseudopotential plane-wave method in the CASTEP package. [29] The electron-ion interactions were described by the norm-conserving pseudopotentials.…”