Problems with \clip

Question

I have a problem with the \clip command. I want to do something like \spy but add some labels etc. only to the magnified picture. Since this is not straightforward, I want to clip a zoomed graph with a circle, but this is not working for me.

Here is the MWE and the graph I could get till now:

\documentclass[border=5pt,tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{calc}
\usetikzlibrary{intersections}
\begin{document}
\def\height{10cm}
\def\width{10cm}
\def\sc{0.8}

\def\xmin{2}
\def\xmax{5}
\def\ymin{0}
\def\ymax{20}   
\def\enlarge{0.05}

\xdef\Gda{12244}
\xdef\aa{1.87}
\xdef\reqa{2.67}
\def\f{0.001}       % scaling factor for values

\begin{tikzpicture}

    \begin{axis}[
        name=plot1,
        height=\height, 
        width=\width, 
        scale only axis=true, 
        scale=\sc, 
        enlargelimits=\enlarge, 
        xmin=\xmin,
        xmax=\xmax,
        ymin=\ymin,
        ymax=\ymax,
        restrict x to domain=\xmin:\xmax,
        restrict y to domain=\ymin:\ymax,
        samples=1000,
        ]

        \addplot[
        color=black,
        smooth,
        ]
        (x,{\f*(\Gda*(1-exp(-\aa*(x-\reqa)))^2)});

        \coordinate (spypoint) at (axis cs: \reqa,1);
        \clip[draw] (spypoint) circle (0.5cm);

    \end{axis}

\end{tikzpicture}

\end{document}

For me and my understanding of \clip, only the picture inside the circle should be shown. It should be an 'easy' mistake, so hopefully someone can help me with this.

** Edit:**

I just add a simple drawing in PPT to show the result of this project, but now, the problem is, that I cannot acess the predefined center of the circle.

I also corrected the code and this is the result so far.

MWE2

\documentclass[border=5pt,tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\usetikzlibrary{calc}
\usetikzlibrary{intersections}
\usetikzlibrary{spy}
\begin{document}
\def\height{10cm}
\def\width{10cm}
\def\sc{0.8}

\def\xmin{2}
\def\xmax{5}
\def\ymin{0}
\def\ymax{20}   
\def\enlarge{0.05}

\xdef\Gda{12244}
\xdef\aa{1.87}
\xdef\reqa{2.67}
\def\f{0.001}       % scaling factor for values

\begin{tikzpicture}

    \clip[draw] (spypoint) circle [radius=4cm]; %<- the predeined point (skypoint) cannot be read, since it is in the axis environment and axis coordinates were used. 

    \begin{axis}[
        name=plot1,
        height=\height, 
        width=\width, 
        scale only axis=true, 
        scale=\sc, 
        enlargelimits=\enlarge, 
        xmin=\xmin,
        xmax=\xmax,
        ymin=\ymin,
        ymax=\ymax,
        restrict x to domain=\xmin:\xmax,
        restrict y to domain=\ymin:\ymax,
        samples=1000,
        xlabel=$\mathrm{r}$,
        ylabel=$\mathrm{V(r)}$,
        ]

        \addplot[
        color=black,
        smooth,
        ]
        (x,{\f*(\Gda*(1-exp(-\aa*(x-\reqa)))^2)});

        \pgfplotsextra{%
            \global \coordinate (spypoint) at (axis cs:\reqa,1);
        }
    \end{axis}


%       \coordinate (spypoint) at (\reqa,1);
        \draw[fill=blue] (spypoint) circle [radius=0.05cm]; %<- here, I labeled the 'correct' center point.
\end{tikzpicture}

\end{document}