Polarizability and charge density distribution in crystalline urea

The aim of this short paper is to document the performance of some one electron Hamiltonians like HF, LDA (S-VWN), GGA (PBE) and Hybrids (PBE0 and B3LYP) in the calculation of the dielectric tensor elements of crystalline urea. Urea crystal has been chosen for two main reasons, first of all it represents a benchmark system for the discussion of linear and nonlinear optical properties of molecular crystals, then, in literature, there is a large variety of experimental and theoretical results to be compared with our calculations. The discussion is supported by electron density deformation maps that give a synoptic representation of the charge reorganization that takes act when passing from isolated molecules to the molecular crystal. The different behavior of the above mentioned Hamiltonians in the description of the electron density of the urea molecular crystal is also analyzed in terms of Born effective charges.