a = 2.5 
Clear[x, y]
A1 = (Sqrt[(1/π)]) Exp[-Sqrt[x^2 + (y - a)^2]]
A2 = (Sqrt[(1/π)]) Exp[-Sqrt[(x - a*Sqrt[3]/2)^2 + (y - 
                      a/2)^2]]
A3 = (Sqrt[(1/π)]) Exp[-Sqrt[(x - a*Sqrt[3]/2)^2 + (y + 
                      a/2)^2]]
A4 = (Sqrt[(1/π)]) Exp[-Sqrt[
              x^2 + (y + a)^2]]
A5 = (Sqrt[(1/π)]) Exp[-Sqrt[(x + a*Sqrt[3]/2)^2 + (y + 
                      a/2)^2]]
\(A6 = \@\(1\/π\)\ Exp[\(-Sqrt[\((x + a*Sqrt[3]/2)\)^2 + \((y - 
                      a/2)\)^2]\)]

\)
Plot3D[A1 + A2 + A3 + A4 + A5 + A6, {x, -3. , 3. }, {y, -3, 3}, 
      PlotPoints -> 31]