Hartree, and 10 -10 Hartree for the frequency analysis. The default DIIS convergence accelerator was applied. In addition, two displacements for each atom along each Cartesian direction were calculated for the phonon modes (NUMDERIV=2) and the IR intensities were calculated based on the Berry phase method. The cohesive energies of both forms were calculated by subtracting the isolated molecular energy from the total solid-state energy considering the basis set superposition error (BSSE), which originates from the finite basis sets. Select normal modes were selected and the corresponding geometries were scanned along the eigenvectors to obtain more information on these modes (SCANMODE). The Gibbs free energy as well as other thermodynamic properties were calculated from 7 K to 300 K for each structure.