Atkins & de Paula:
Physical Chemistry for the Life Sciences
The variation of the energy of interaction (on the electrostatic model) of a hydrogen bond as the angle between the O--H and O...O directions is changed is given by
Where A is the constant 
(J m mol-1), zO and zH
are the partial charges on O and H, 
is the angle (degrees), and R and r are in meters.
To graph the bond energy (J mol-1) enter the parameters (i.e., zO, zH, R, r) and hit New Plot.
Up to 5 plots can be displayed at one time. The Clear button will remove all plots. To see the parameters
for each plot hit the Legend on/off button. The Redraw button will refresh the graph. This is useful when
the function domain (i.e., ) has been changed. To see the value of each plot
at a given point, move your cursor to the desired location then click and hold.