Vibrational, thermodynamic, and dielectric properties of ε-CL-20: first-principles calculations.

The DFT theory is used to investigate the vibration forms of ε-CL-20 by discussing the phonon DOS and infrared and Raman spectra. By observing them, the detailed vibration forms can be obtained, and the vibrations are different in the different regions. Our calculated vibrational results are consistent with previous data. In order to deeply comprehend CL-20, we also investigate the thermodynamic properties, finding that entropy, enthalpy, Debye temperature, and heat capacity are increased with the rising temperature and the vibrational free energy decreases with the increasing temperature. The εxx, εyy, and εzz are similar, which reflects the small anisotropy among [100], [010], and [001]. Moreover, it can be noticed that the major contribution for static dielectric constants originates from the electronic contribution.