All-electron density-functional studies of hydrostatic compression of pentaerythritol tetranitrate C(CH2ONO2)4

Abstract

All-electron calculations of the hydrostatic compression of pentaerythritol tetranitrate C(CH2ONO2)4(PETN) crystal have been performed using density-functional theory with the PBE functional in conjunction with the 6-31G** Gaussian basis set. Full optimizations of the atomic positions and ratio of lattice parameters c/a for the tetragonal crystal were performed for eight volume ratios 0.65≤V/V0≤1.00, where V0 is the equilibrium volume at zero pressure. The pressure, linear compressibilities of lattice parameters a and c, and c/a ratio as functions of volume ratio are in good agreement with experiment. It is observed that c/a decreases monotonically with compression until V/V0=0.8 and then increases monotonically for all higher levels of compression considered. Changes in intramolecular coordinates and close intermolecular contact distances were studied as a function of compression. The results indicate essentially rigid-molecule compression for V/V0>0.8, with the onset of significant intramolecular distortion for higher compressions. Predictions of the bulk modulus B0 and its pressure derivative B0′ were obtained using various equation of state fitting forms. Values for these quantities are compared to experiment and to the results of a preceding molecular simulation study of PETN based on an empirical force field. © 2004 The American Physical Society.