As shown in Figure .a, these included specific stiff dihedrals (χ and ξ ), described through equation ( ) and specifically defined for both Ni coordination atoms (two Oxygen and two Nitrogen), and the lateral aromatic rings. The resulting system of 61 independent parameters, was optimized with a final standard deviation of 0.1 kJ/mol. Given the fairly stiff scaffold and the absence of low vibrational modes, the parameterization was carried out in a single step, based on the optimized QM geometry and Hessian matrix only. Figure shows the standard preliminary validations tests, where it appears that both the optimized geometry and the vibrational features described by the QMD-FF are in good agreement with the reference QM data.