with a coupling constant of 1 ps. Then, an NVT simulation of 20 ns was performed with the same thermostat as previously described. In both the NVT and NPT simulations, the particle mesh Ewald (PME) approach was used to model electrostatic interactions with a long-range cutoff of 1.5 nm. Lennard-Jones interactions were also modeled with the same cutoff of 1.5 nm. The time step for the MD simulations was 2 fs. The backbone of DNA was restricted using a position constraint of 1,000 kJ•mol -1 nm -2 . Finally, the final snapshot structure was optimized with respect to the adopted molecular mechanics (MM) force field and from which three model systems were constructed as described in detail in the subsequent section. These preparatory calculations were carried out with use of the Gromacs program. In the spectrum simulations, the def2-SVP 54 basis set was employed for all atoms belonging to the G-quadruplex, including the potassium ions. The largest model system has in addition to this core region also an embedding region consisting of (i) a QM solvation shell for which the STO-3G 55 basis set was employed for water molecules and sodium ions and