On how to find the norming constants for the maxima of a folded normally distributed variable

A general procedure when one is looking for a limiting distribution of X_n = max(X_1,\ldots, X_n) is to first center X_n by subtracting c_n and then scale by d_n (Mood et al.,1974). This article is focused on finding the norming constants c_n and d_n for the maxima of
the folded normal random variable X_n, where X = |Z| , Z\sim N(0, 1) . We also show that
after appropriate normalisation, X_n has a limiting distribution H(x) =\ exp(\exp(x)),
which is the Gumbel distribution.