Semiempirical molecular orbital method repulsive energy

There is little to report on the application of molecular orbital calculations to this class of heterocycles. Yamaguchi et al. <91AX(C)590> have observed that the semiempirical AMI method underestimates the double bond character of the bicyclic C—C bond in 2-phenyl-1,2,3-triazolo[4,5-e][l,2,3,4]tetrazine (24) (Table 1). The AMI method has been reported to overestimate bond lengths in other nitrogen heterocycles <92JCS(P1)2779>, and this is possibly attributable to an overestimation of core-repulsion energies for multinitrogen systems. 

The atom superposition and electron delocalization molecular orbital (ASED-MO) method is a semiempirical approach used to predict molecular strucures, stabilities, force constants, electronic properties, and reaction pathways (466-472). The molecular binding energy, E, involved in chemical bond formation is regarded as a sum of repulsive atom superposition energy, and an attractive electron delocalization energy, Eq that is,... 

The simplest semiempirical w-electron theory is the free-electron molecular-orbital (FE MO) method, developed about 1950. Here the interelectronic repulsions l/r,y are ignored, and the effect of the cr electrons is represented by a particle-in-a-box potential-energy function V" = 0 in a certain region, while V = oo outside this region. With the interelectronic repulsions omitted, in (16.1) becomes the sum of Hamiltonians for each electron hence (Section 6.2)... 

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