Keyword CPSEARCH

This keyword activates the critical point search of scalar molecular fields. For the definition of the search region, see the keywords BOX (4.10.7) and POINTS (4.10.8).
Options:

$<$FIELD$>$

Scalar molecular field specification. The available field acronyms are RHO and ESP. See Table 12 for the acronym meanings. This specification is mandatory, even though the syntax is that of an option!

BASIS / AUXIS

	BASIS		The Kohn-Sham density is used for the calculation of the scalar molecular field. This is the default.
	AUXIS		The auxiliary function density is used for the calculation of the scalar molecular field. Only available in combination with the ESP option.

Description:
The critical points of the density (RHO) and molecular electrostatic potential (ESP) can be searched with this option. By default, the critical point search is performed in a marching cube-like style [281]. In it, the molecule is embedded in a rectilinear box (BOX LARGE; see Section 4.10.7), which in turn is divided into subboxes. Each subbox is searched for a critical point [282]. The box size and shape can be manipulated by the BOX keyword.

As an alternative, start points for the critical point search can be supplied by the POINTS keyword (see Section 4.10.8). With the POINTS option, POLYGON start points between atom pairs and triples are generated automatically. This option is recommended for the critical point search of the density. In addition to the critical point search, the molecular connectivity over (3,-1) critical points is generated [38]. Figure 15 depicts critical point search results for Li$_5$. The two left-hand graphs show the non-nuclear attractors and bond critical points of the electron density in this system. The molecular graph from the density is also depicted to guide the eye. The figures were rendered with VU [41]. The right-hand two graphs in Figure 15 depict the bond critical points and minima of the molecular electrostatic potential (MESP). Again the molecular graph, however now derived from the molecular electrostatic potential, is also depicted.

Figure 15: Non-nuclear attractors (left) and bond critical points (middle left) of the density in Li$_5$. For comparison, the bond critical points of the MESP (middle right) and MESP minima (right) are also depicted.