Elastic properties of molecular crystals using density functional calculations

elastic properties of several molecular crystals (PE, PETN, urea) have been investigated using plane-wave pseudopotential methods based on density functional theory (DFT). The lattice constants, elastic constants and bulk modulus of the molecular crystals were calculated and compared with experiments. Two prevalent density functional methods, LDA and GGA-PBE were tested and compared with each other. We find that LDA typically overestimates the stiffness of these crystals at least by factor of two, while the GGA calculations with the PBE exchange-correlation functional are more reasonable. A large cutoff of the plane-wave basis and a modest sampling of k space are required to describe the molecular crystals. The elastic behavior of urea and PE crystals under uniaxial compressions show interesting anisotropic effects.