An array specifying the atom pairs that will be skipped when constructing the neighbor
list.  This effectively remove the interaction between the atom pairs, and is one way
to prepare a crack.

<p>
Format: <tt>nl_skip_pairs = [ <i>n  i<sub>1</sub> j<sub>1</sub> i<sub>2</sub> j<sub>2</sub> 
 &hellip; i<sub>n</sub> j<sub>n</sub></i> ] </tt>
<br>
where <tt><i>n</i></tt> indicates the number of pairs, followed by the indices of the atom pairs.

<p>
This array is usually not set manually, but is set automatically by commands <tt>cutbonds</tt>
and <tt>cutbonds_by_ellipse</tt>.
