AMI model

The orbital coefficients obtained from Hiickel calculations predict the terminal position to be the most reactive one, while the AMI model predicts the Cl and C3 positions to be competitive. In polyenes, this is true for the addition of nucleophilic as well as electrophilic radicals, as HOMO and LUMO coefficients are basically identical. Both theoretical methods agree, however, in predicting the Cl position to be considerably more reactive as compared to the C2 position. It must be remembered in this context that FMO-based reactivity predictions are only relevant in kinetically controlled reactions. Under thermodynamic control, the most stable adduct will be formed which, for the case of polyenyl radicals, will most likely be the radical obtained by addition to the C1 position. 

Both 3-21G and 6-3IG Hartree-Fock models provide better and more consistent results in supplying reactant and transition-state geometries than the AMI calculations. Also the two Hartree-Fock models (unlike the AMI model) find reasonable transition states for all reactions. With only a few exceptions, activation energies calculated using approximate geometries differ from exact values by only 1-2 kcal/mol. 

Figure 2.8 Synthesis of Scherer s sterically highly hindered, extremely persistent perfluoroalkyl radicals 11 and 12. The AMI model above) indicates the bulky structure of 11 [8],...

Excited electronic states of l,6,6a2 -trithiapentalenes were calculated in order to explain the orange color of the compound which is not observed with carbocyclic 10 r-electron systems. Quantum chemical configuration interaction calculations using the AMI model and ab initio Hartree-... 

Shapiro, J. R, Bottom-up vs. Top-down Approaches to Supply Chain Management ami Modeling, Sloan School of Management, Massachusetts Institute of Technology, Cambridge, MA, 1998. 

With only s- and p-functions present, the two-centre two-electron integrals can be modelled by multipoles up to order 4 (quadrupoles), however, with d-functions present multipoles up to order 16 must be included. In MNDO/d all multipoles beyond order 4 are neglected. The resulting MNDO/d method typically employs 15 parameters per atom, and it currently contains parameters for the following elements (beyond those already present in MNDO) Na, Mg, Al, Si, P, S, Cl, Br, I, Zn, Cd and Hg. Recently this technology has been used in connection with the AMI model as well, which at least for phosphorous yields a further improvement. ... 

Figure 9. (A) Structures and atom labeling of naphthalene and bridged naphthalene dimer molecules. Molecular geometries were optimized using AMI model in Gaussian 98 package 2 (B) UV absorption spectra of the DN n series. Top experiment. Bottom linear absorption profile calculated with line width Fy = 0.2eK Computed absorption spectra are shown in arbitrary units Contour plots of electronic modes which dominate the absorption spectra of DN-n. The axis labels represent the individual carbon atoms as labeled in the molecular templates (A). Reprinted with permission from ref 342. Copyright 1999 National Academy of Sciences, U.S.A.

It needs to be noted as well that a number of special pairwise potential functions (0-H, N-H, etc.) exist in the AMI model. Unfortunately, these were never codified in a publication. The form and constants for the functions may be found in public domain versions of programs containing the AMI method (i.e., MOPAC or older versions (pre 4.0) of AMPAC). 

AMI model investigation of 3-methyl-4-nitroaniline crystal. /. Phys. Chenu A, 105, 1366-1370. 

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