Fig. 2: The transform function and its derivative.
From: Hamiltonian transformation for accurate and efficient band structure interpolation
a The transform function fa,n(x) for different values of n, with the transition region width a = 1. As n increases, fa,n(x) becomes smoother. b The derivative \({f}_{a,n}^{{\prime} }(x)\). Higher values of n result in a more gradual change in slope.
