A first-principles investigation of the equation of states and molecular "weak spots" of $\beta$-cyclotetramethylene tetranitramine (HMX)

TL;DR

This study uses first-principles DFT-D2 calculations to analyze the equation of states of $eta$-HMX, revealing pressure-sensitive N-N bonds and emphasizing the importance of van der Waals interactions in modeling this energetic crystal.

Contribution

It provides a detailed first-principles analysis of $eta$-HMX's structural response under pressure, identifying molecular weak spots and highlighting vdW interactions' significance.

Findings

N-N bonds along the minor axis are pressure-sensitive

Van der Waals interactions are crucial for accurate modeling

Identified potential molecular weak spots in $eta$-HMX

Abstract

We investigate the equation of states of the $\beta$-polymorph of cyclotetramethylene tetranitramine (HMX) energetic molecular crystal using DFT-D2, a first-principles calculation based on density functional theory (DFT) with van der Waals (vdW) corrections. The atomic structures and equation of states under hydrostatic compressions are studied for pressures up to 100 GPa. We found that the N-N bonds along the minor axis of the ring are more sensitive to the variation of pressure, which indicates that they are potential "weak spots" in atomic level within a single molecule of $\beta$-HMX. Our study suggested that the van der Waals interactions are critically important in modeling this molecular crystal.