“…Different from experiments, a quantum mechanical (QM) screening allows to get structures and properties of copigmentation systems (Quartarolo and Russo, 2011 ; Di Meo et al, 2012 ; Kalisz et al, 2013 ; Rustioni et al, 2013 ; Trouillas et al, 2015 , 2016 ), such as binding energies and spectral shifts, in a quicker, time-saving and money-saving way. This implies the use of a reliable theoretical model which consists in a good strategy for searching the most stable conformers of copigmentation complex in the conformational space, in an appropriate choice of the QM methods for geometry optimization, energetic and spectral calculations and in a reliable description of solvation effects (Li et al, 2011a , b ; Nave et al, 2012 ; Rustioni et al, 2013 ; Trouillas et al, 2015 , 2016 ; Marpaung et al, 2017 ). Actually, finding out the most stable conformer can be done by calculations totally based on a QM approach, starting from few most probable orientations, or by a preliminary molecular dynamics (MD) simulation followed by a QM refinement (Di Meo et al, 2012 ; Trouillas et al, 2015 , 2016 ).…”