Vibrational and thermodynamic properties of β-HMX: a first-principles investigation
Zhongqing Wu1, Rajiv K Kalia, Aiichiro Nakano
1Collaboratory for Advanced Computing and Simulations, Department of Physics & Astronomy, University of Southern California, Los Angeles, California 90089-0242, USA.
Abstract:
Thermodynamic properties of β-HMX crystal are investigated using the quasi-harmonic approximation and density functional theory within the local density approximation (LDA), generalized gradient approximation (GGA), and GGA + empirical van der Waals (vdW) correction. It is found that GGA well describes the thermal expansion coefficient and heat capacity but fails to produce correct bulk modulus and equilibrium volume. The vdW correction improves the bulk modulus and volume, but worsens the thermal expansion coefficient and heat capacity. In contrast, LDA describes all thermodynamic properties with reasonable accuracy, and overall is a good exchange-correlation functional for β-HMX molecular crystal. The results also demonstrate significant contributions of phonons to the equation of state. The static calculation of equilibrium volume for β-HMX differs from the room-temperature value incorporating lattice vibrations by over 5%. Therefore, for molecular crystals, it is essential to include phonon contributions when calculated equation of state is compared with experimental data at ambient condition.
Related Concept Videos
Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
According to Hooke's law, the vibrational frequency is directly proportional to the...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
¹H NMR: Complex Splitting
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Stability of Substituted Cyclohexanes
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene


