The DFT simulations were performed using the CRYSTAL17 software package. The published crystallographic data from the Cambridge Structural Database (CSD) (ACSALA07; ACSALA17) were used to set the initial atomic positions and lattice parameters. The subtle differences between the two polymorphs required very strict parameters for the best differentiation. The "extra extra large" grid (XXLGRID) was used to generate 100 k-points in reciprocal space (SHRINK=7) and the tolerance of bielectronic coulomb and Hartree-Fock (HF) exchange integrals were set to 10 -12 , 10 -12 , 10 -12 , 10 -12 and 10 -24 (TOLINTEG). The atomic centered triple-𝜉 Ahlrichs' VTZ basis set (with polarisation) and the PBE density functional with Grimme-D3 London dispersion correction were applied with a three body Axilrod-Teller-Muto repulsion term (ABC) . The energy convergence criterion for the geometry optimisation was set at 10 -8