我正在尝试创建下图。但是，我在制作右图上的曲线顶部时遇到了困难。具体来说，我该如何制作一个长命令来绘制阴影曲线，而不是两个单独的命令并在中间添加一条随机线？我的 MWE 如下所示：
\documentclass[tikz,border=3mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes,
arrows.meta,
calc,
positioning,
decorations.pathreplacing,
decorations.markings,
calligraphy,
bending,
shapes.geometric,
3d,
tikzmark,
fit,
matrix,
shapes.misc}
\usepackage{pgfplots}
\usepackage{pgf}
\usepackage{amsmath} %Note I do not know what other packages are necessary since I have my own package that already has everything I need in it.
\begin{document}
\begin{tikzpicture}
\draw[Latex-Latex,thick] (0,5.5) node[above]{$E$/eV} -- (0,0) -- (4,0) -- (4,5.5);
\draw[thick,-Latex] (4.5,5.5) -- (4.5,0) -- (8.5,0);
\draw[thick] (0,-0.1) node[below]{0} -- (0,0.1);
\draw (2,-0.1) node[below]{$k$};
\draw[thick] (4,-0.1) node[below]{$\frac{\pi}{a}$} -- (4,0.1);
\draw (6.5,-0.1) node[below]{\textsc{dos}, $N(E)$};
\draw[dotted,thick] (0,4) -- (8.5,4) node[right]{$E_F$};
\draw[thick] (0,0.25) ..controls +(0:2.5) and +(180:1.5).. (4,1.5)
node[pos=0.75,inner sep=0pt](s){};
\draw[thick] (0,3.4) ..controls +(0:3) and +(180:1.5).. (4,3.65)
node[pos=0.75,inner sep=0pt](px){};
\draw[thick] (0,3.5) ..controls +(0:3.0) and +(180:1.5).. (4,3.75)
node[pos=0.75,inner sep=0pt](py){};
\draw[thick] (0,4.5) ..controls +(0:3) and +(180:1.5).. (4,3)
node[pos=0.75,inner sep=0pt](pz){};
\node[xshift=-2em] at (s) {$2s$};
\node[] at (0.8,3.1) {$2p_x$, $2p_y$};
\node[] at (0.4,4.8) {$2p_z$};
\draw [fill=black!25] (4.5,0.25) -- +(1.5,0.0) .. controls +(-1.2,0.25) and +(-1.2,-0.25) .. +(1.5,1.5) -- +(0.0,1.5) -- cycle;
\draw [fill=black!25] (4.5,3) -- +(1.5,0.0) .. controls +(-1.2,0.2) and +(-4,-0.25) .. +(3.75,0.7) -- +(0.0,0.7);
\draw [fill=black!25] (4.5,3.7) -- +(3.75,0) .. controls +(-1.5,0.15) and +(-1.2,-0.35) .. +(0.75,0.3) -- +(0,0.3); %I want to connect this with
\draw [fill=black!25] (4.5,3) -- +(1.5,0.0) .. controls +(-1.2,0.2) and +(-4,-0.25) .. +(3.75,0.7) -- +(0.0,0.7); %this curve without horizontal line.
\end{tikzpicture}
\end{document}