Molden can display the laplacian of the electron density when
used with the Ab Initio packages GamessUS/UK and Gaussian.
The laplacian of the electron density is the trace of the Hessian matrix.
Or in plain(er) language, the sum of the diagonal elements of the second
derivative matrix of the density. The laplacian provides interesting
information about the chemical bond. This approach has been pioneered by
Bader. Have a look at his excellent lecture on
The Theory of Atoms in Molecules.
The characteristics of the laplacian can be summerized a follows:
Three commandline flags were introduced to aid the space type of plots of the laplacian.
-L display both neg. and pos. contour in space plot of the laplacian. Default only the value specified with "space=value" will be rendered. -1 use only the lower half of the cubic grid used for the space type plot -2 use only the upper half of the cubic grid used for the space type plot
The latter two were introduced to increase the visibility of the inner (enclosed by other surfaces) surfaces.
Laplacian 3D plot file=clf3.out laplacian edge=9.0 phase=-1 postscript 3D
Figure 2 shows a Euclid plot of the Laplacian of CO using a minimal basis set.
Figure 3 shows a VRML plot of the Laplacian of CO using a minimal basis set. It was constructed with -1 molden commandline flag. Clicking on figure 3 will bring up the VRML scene.