Figure 1

(a) The monoclinic phase of melamine (P21/a with Z = 4) in stick representation, according to plane-wave DFT (PBE-TS) optimization at 0 K. Atom color coding: hydrogen (white), nitrogen (blue) and carbon (grey). Red dashed lines indicate hydrogen bonding. (b) Temperature dependence of the molar heat capacity for the P2/1a phase of melamine according to selected density functional theory approximations. The scatter plot comes from the experimental data of Stephenson41 (Calorimetry I) and Peng et al. (Calorimetry II)42. The theoretical results are based on harmonic phonon dispersion calculations presented in this work. See text for details.