Ab initio study of naphthalene and anthracene elastic properties

A study of the crystal structure, mechanical and acoustic properties of two P2(1)/a and P2(1)/c monoclinic phases of naphthalene and anthracene was performed using ab initio method of linear combination of atomic orbitals (LCAO) and basis sets: C_6-21G*, H_3-1p1G. The method was implemented in the CRYSTAL'14,'17 software package using electron density functional theory including van der Waals interactions (DFT-D2 and DFT-D3 (BJ)), in the local density approximation (LDA) with VWN exchange-correlation potential, gradient approximation PBE exchange-correlation functional and B3LYP hybrid functional. The calculated elastic constants for the first time are in moderate agreement with experimental data. Bulk modulus B, shear modulus G, Young's modulus E and the Poisson's ratio mu, as well as acoustic properties (average velocity of sound < v >, the Debye temperature Theta(D), and acoustic Gruneisen parameter gamma(a)) were obtained using the Voigt-Reuss-Hill model.