First-principles study of the crystal structure and equation of state of naphthaline and anthracene
A first - principles method of density functional theory with a gradient approximation of the exchange-correlation potential in the form of PBE implemented in the PWscf program of the Quantum ESPRESSO software using the Grimme′06 scheme is used to calculate the crystal structure of naphthaline and anthracene at a hydrostatic pressure ranging from 0 GPa to 2 GPa and from 0 GPa to 20 GPa respectively; their equations of states are analyzed. It is shown that under pressure the volume decreases due to voids, and the molecules themselves are practically not deformed. The Grüneisen parameter is calculated in the Slater-Dugdale-MacDonald-Zubarev-Vashchenko model. This parameter decreases from the equilibrium values of 2.356 (anthracene) and 3.226 (naphthaline) with an increase in the pressure. With the use of the Mie-Grüneisen equation under the additional Hugoniot-Renkin condition the impact pressure is calculated, which increases compared to the cold one at a relative compression V/V0, below 0.7.