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

Abstract

All-electron calculations of the hydrostatic compression of pentaerythritol tetranitrate C(CH 2 ONO 2 ) 4 (PETN) crystal have been performed using density-functional theory with the PBE functional in conjunction with the 6-31 G** 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/V 0 ≤1.00, where V 0 is the equilibrium volume at zero pressure. The pressure, linear compressibilities of lattice parameters a and c, and cla ratio as functions of volume ratio are in good agreement with experiment. It is observed that c/a decreases monotonically with compression until V/V 0 =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/V 0 >0.8, with the onset of significant intramolecular distortion for higher compressions. Predictions of the bulk modulus B 0 and its pressure derivative B' 0 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.