Abstract
Incommensurate structures can be described by the Frenkel-Kontorova model. Aubry has shown that, at a critical value Kc of the coupling of the harmonic chain to an incommensurate periodic potential, the system displays the analyticity-breaking transition between a sliding and pinned state. The ground-state equations coincide with the standard map in non-linear dynamics, with smooth or chaotic orbits below and above Kc, respectively. For the standard map, Greene and MacKay have calculated the value Kc = 0.971635. Conversely, evaluations based on the analyticity breaking of the modulation function have been performed for high commensurate approximants. Here we show how the modulation function of the infinite system can be calculated without using approximants but by Taylor expansions of increasing order. This approach leads to a value Kc' = 0.97978, implying the existence of a golden invariant circle up to Kc' > Kc.