refers to stiff torsions (st). Within the JOYCE protocol, it is often employed to describe dihedrals φ (as for instance those ruling the planarity of aromatic rings or conjugated double bonds), whose internal energy variation is better described by such an harmonic term with respect to the Fourier-like series usually employed by transferable FFs. In most large-sized molecules, however, the effectiveness of a local harmonic approximation (LHA) cannot be fully exploited. This is because these species are very often characterized by flexible "soft" coordinates, i.e.