In the last fifty years. computational chemistry has made impressive strides. Huckel NO computations were rapidly succeeded by semiempirical monodeterminantal Self Consistent Field (SCF) MO calculations which now give way to high quality ab initio calculations of the poly-determinantal SCF-MO and Generalized VB variety.  Meer

The bond diagrammatic representation of molecules is the foundation of MOVB theory. To a certain extent, this kind of representation is analogous to the one on which "resonance theory" is based and this fact can be projected by a comparison of the various ways in which MOVB theory depicts a species made up of three core and two ligand MO's which define two subsystems containing a total of six electrons and the ways in which "resonance theory" (i.  Meer