MNDO calculations association

Whereas these studies have established the gross structural changes associated with the Pg and P7 transportation pathways, MNDO calculations have provided insights into the electronic details of the strucmral changes occurring on the ground- and excited-state transposition coordinates [16]. 

Fig. 4. Illustrative perspective views of density distributions corresponding to the valence-shell MO right column) and the associated NoO left column) for water molecule, from standard MNDO calculations (from Ref. [48]) only contours below the molecular plane are shown. The MO are ordered in accordance with increasing orbital energies for NoO the increasing criterion has been adopted...

The mixed (heterogeneous) complexes of a lithium amide (LDA or LiTMP) and a ketone lithium enolate (acetone, cyclohexanone or diisopropyl ketone) have been examined by semiempirical methods (MNDO) by Romesberg and Collum48. If the stabilization associated with these mixed complexes was not determined, the solvation (by THF and HMPA) of the mixed cyclic dimers and trimers was calculated to be generally exothermic (but decreasingly with the steric demand of the enolate) and led to disolvated entities. A set of solvated dimers, trimers and tetramers, cyclic or not, has thus been identified... 

Semiempirical methods, for example, MNDO. AMI, and PM3. are simplifications of ab initio molecular orbital theory and employ empirically determined parameters in essence, they only differ in the approximations being made. These methods involve adjustable parameters associated with molecular properties that are calibrated against experimental data. The chief advantage of semiempirical calculations over ab initio calculations is that they are several orders of magnitude faster. Thus, calculations for systems of up to c. 200 atoms are currently possible, whereby with ab initio methods, the limit is a moderately sized molecule (about 50 atoms at the time of writing), if rational results are to be obtained. Frequently, semieinpirical methods have proved to be the computational procedures of choice for studying relatively large molecules. 

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