hard wall and soft wall models is that the experimental results available for charmonium and bottomonium vector states show that higher excited radial states have smaller decay constants. In other words, $f_n$ decrease with $n$. In contrast, the results obtained for decay constants of vector mesons in the soft wall are degenerate: all the decay constants of the radial excitations of a vector meson are equal. For the hard wall model the decay constants of radial excitations increase with the excitation level. A fit of the decay constants of charmonium states in soft wall appeared in ref. [@Grigoryan:2010pj], but introducing three extra parameters in the model. In ref. [@Grigoryan:2010pj] four experimental data, the masses and decay constants of $J /\psi $ and $\psi^\prime$, are used to fix four parameters introduced in the model, thus the formulation lacks of predictivity as a model for heavy vector mesons.

An alternative version of the soft wall model, consistent with the observed behavior of decay constants, was recently proposed in ref. [@Braga:2015jca]. In contrast to the original formulation, in this new framework the decay constants are obtained from two point correlators of gauge theory operators calculated at a finite value $ z = z_0$ 