# Custom Ticks in 2D Plot

I'm having trouble customizing the ticks on a 2D plot.

I currently have:

Plot[{1/8(4-4x/(5.2917721067*10^(-11))-x^2/(5.2917721067*10^(-11)^2))\
e^(-x/5.2917721067*10^(-11))}, {x,0,15*5.2917721067*10^(-11)}]


I want to customize the ticks such that it shows a tick at every interval of a0 = 5.2917721067*10^(-11) (hence the 0 -> 15*a0).

However, when I try to do:

Plot[{1/8(4-4x/(5.2917721067*10^(-11))-x^2/(5.2917721067*10^(-11)^2))\
e^(-x/5.2917721067*10^(-11))}, {x,0,5.2917721067*10^(-11)}, Ticks ->
{{5.2917721067*10^(-11), a0}, {2*5.2917721067*10^(-11), 2a0}...}]


It fails to even plot the correct graph; it attempts to plot a straight line defined by:

Plot 5.2917721067


Is there something I'm missing?

a0 = QuantityMagnitude[UnitConvert[Quantity[1, "BohrRadius"]]];