Vdw displays the van der Waals surface for the atoms in atom-spec. The vdw command may be interrupted by the Esc key. Atoms whose vdw surfaces were already computed when the interrupt occurred will have their surfaces displayed. Since computing the vdw surface is faster than displaying it, pressing the Esc key might not help.
The default radii depend on whether explicit hydrogen atoms are present. When there are no explicit hydrogens, the radii of some atoms are enlarged to compensate. VDW radii can be altered with vdwdefine and the density of dots can be changed using vdwdensity.
Details of the vdw algorithm can be found in:
P.A. Bash, N. Pattabiraman, C.C.Huang, T.E. Ferrin, and R. Langridge, "Van der Waals Surfaces in Molecular Modeling: Implementation with Real-Time Computer Graphics" Science 222:1325 (1983).
See also: surface, vdwdefine, vdwdensity