The mixed electric-magnetic dipole tensor, G, is evaluated in the velocity gauge as given in the second expression. Furthermore, it is complex and calculated with a damping term, In Fig. , we have plotted the CD spectra obtained for the three systems. For the small and medium model systems, spectra have been obtained both with a resolution of the 40 lowest excited singlet states (bars and solid line) as well as with the CPP method (circles). For the large system, only the CPP method was used. The three models present a clear bisignated signal characteristic of the G-quadruplex. When incorporating the sugar moiety to the G-quadruplex (from small to medium), we observe a slight red-shift of 15 nm and an increase of the peak intensities but the overall shape of the spectra is not affected. To better understand the nature of the transitions at play, we focused on the medium system and looked at the attachment and detachment densities for four transitions that are shown in panels A-D in Fig. . We looked at these representative transitions for both the positive and negative peaks (two for each) and performed an analysis using a tool for visual analysis of electronic transitions that has been implemented in a local version of the VIAMD software. We separated the three guanine layers into separate groups, referred to as "bottom", "middle", and "top" in Fig. , and the transition diagrams show the percentage involvement of the three groups in the electronic excitations. It is clear that these four transitions are local in character as virtually no charge transfer can be observed in between layers. Looking at the densities, it is also very clear that the excitations are predominantly localized to the guanines leaving the sugars to play a spectator role. While the two transitions contributing to the positive peak are mainly localized to the middle layer (panels A and B in Fig. ), the two transitions contributing to the negative peak have important contributions from the bottom and top layers (panels C and D in Fig. ).