DNA Proton Tunneling

The hydrogen bond holding a DNA base pair together is not a rigid link — the shared proton sits in a double-well potential and, being light enough to behave quantum mechanically, can tunnel between its normal ("canonical") position and a rare tautomeric position on the other side of the bond. This simulator solves the real time-dependent Schrödinger equation for that proton with a split-step Fourier integrator, rendering the live probability density |ψ(x)|² along the hydrogen-bond axis between two schematic bases. Switch between A–T and G–C pair geometries, tune the barrier height and the tautomer energy asymmetry, and swap the proton for a deuteron to see the kinetic isotope effect throttle the tunneling rate — the same double-well mechanism Löwdin proposed in 1963 as a quantum-mechanical route to spontaneous point mutations during replication.