Modeling solid–solid phase transitions in PETN using density functional theory

Abstract

We present density functional theory (DFT) calculations of a stable orthorhombic phase of hydrostatically compressed pen-taerythritol tetranitrate (PETN). In these calculations, an orthorhombic (a ≠ b ≠ c) structure optimized at a very high pressure was used to initialize crystal structure optimizations at progressively lower pressures until the optimization spontaneously reverted to a tetragonal phase (a = b ≠ c). The orthorhombic crystal structures exhibit P21212 symmetry and a lowering of molecular symmetry from S 4 to C2, which matches the orthorhombic PETN III phase debated in the literature. These findings are consistent across several DFT methods; however, the predicted transition pressures range from 16 to 23 GPa depending on the type of the functional and the size of the periodic supercell.