**Figure 3**
Density slices from (*a*) a binary model mask and (*b*) the corresponding Gaussian model mask (the polynomial model mask is similar and is not shown) derived from test model 1exr
. The coloring scheme is from red (zero density) through white (0.5 density level) to blue (1.0 density level). Below each density slice is a one-dimensional representation of the mask for each case, given a single atom at the origin. The distance from the atom in Å is given on the *x* axis and the *y* axis depicts the relative electron density of the mask. In (*d*), the Gaussian model (*A* = 11.5 Å, σ = 0.55 times the van der Waals radius) is shown in blue and the polynomial model (*a* set to the van der Waals radius, *w* = 0.8 Å) is shown in magenta given an atom with a van der Waals radius of 1.75 Å. |