Model system is shown on *Fig. 3.*.
Effective surface of electrodes (*Cf. Fig. 4.*) is assumed to be
outside the geometric surface.

**Figure 3:**
Model system.
Geometric surface of the support, tube, and tip.

**Figure 4:**
Comparison of effective and geometric surfaces of
electrodes. Effective surface (green line)
is
outside of the geometric surface (black line).
Dimensions are in *nm*.

Geometric line cut is shown in *Fig. 5.*.
It is defined as the line drawn by
the tip apex point
( (*X*_{apex}, *Z*_{apex}),
when the distance of the nearest point of the sample and tip
is the (pre-selected) constant value.
When the tip is far from the nanotube the line cut
is a horizontal line above the support surface. In this case the
nearest point of the tip to the sample is the tip apex point.
When the tip approaches the nanotube (at
) the nearest tip point to the sample becomes a point on the side
of the tip and the nearest sample point to the tip will be a
point on the side of the nanotube.

**Figure 5:**
Geometric line cut.
Red line is the geometric line cut drawn by the
tip apex (marked by open circle).
Shaded lower half plane, middle ring and
upper hyperbolas show the vertical cross
sections of sample, nanotube, and tip.
Electrodes are bounded by their jellium
surfaces (green lines).
Several, typical tip positions are shown, with
different colors.
For each tip position, nearest tip and
sample points are joined by a thin dashed line.