The valence bond (VB) theory uses localized orbitals,
and its wave
function is composed of a linear combination of various VB structures
which are based on sets of spin functions. The VB structures are not
unique, and different sets are used, Rumer sets being the most common
for classical VB due to their advantage as being both easily obtained
as linearly independent and meaningful. Yet, Rumer rules, which are
responsible for the simplified process of obtaining the Rumer sets,
are very restrictive. Furthermore, Rumer sets are best suited for
cyclic systems; however, in noncyclic systems, structures resulting
from Rumer rules are often not the most intuitive/suitable structures
for these systems. We have developed a method to obtain chemically
insightful structures, which is based on concepts of chemical bonding.
The method provides sets of VB structures with improved chemical insight,
which can also be controlled. Parallel to the Rumer structures, the
chemical insight sets of structures are based on electron pair coupling,
and hence, pictorially can be drawn similarly to the Lewis structures.
Yet, different from Rumer rules, the chemical insight method, being
more flexible, allows larger combinations of bonds as well as larger
combinations of structures in the sets it offers, resulting in many
more possible sets that are better adapted to the systems studied.