Infinite square well

a = 1
psi[n_, x_] := Sqrt[2/a]*Sin[n*Pi*x/a]
En[n_] := n^2

Do[
label = 
        StringJoin["n = ", ToString[n]]; 
pl[n] = 
        Plot[psi[n, x], {x, 0, 
            a}, 
PlotRange -> {{-0.5, 
                1.5}, {-1.5, 
                1.5}}, 
Ticks -> {{-0.5, 0.5, 
                1}, {-1, 0, 
                1}}, 
DisplayFunction -> 
            Identity, 
Epilog -> 
            Text[label, {1, 1.3}]], 
{n, 1, 6}]

Show[
      GraphicsArray[{{pl[1], pl[2], pl[3]}, 
{pl[4], pl[5], 
            pl[6]}}], 
DisplayFunction -> $DisplayFunction]

Psi[x_, t_] := 
      1/Sqrt[2] psi[4, x] Exp[-I*En[4] t]
 + 
        1/Sqrt[2] psi[5, x] Exp[-I*En[5] t]
rho[x_, t_] := Abs[Psi[x, t]]^2

Do[Plot[
        rho[x, t], {x, 0, 
          1}, 
PlotRange -> {{-0.2, 
              1.2}, {-0.5, 4}}], 
{t, 0, 2, 
        0.1}]