General Performance Overview of Basic NDDO Models

In addition to the twelve elements noted above, PM3 parameters for Li, Be, Na, Mg, Ca, Zn, Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, Hg, Tl, Pb, and Bi have been reported. The PM3 methodology is available in essentially all molecnlar modeling packages that carry out semiempirical calculations. 

6 General Performance Overview of Basic NDDO Models 

Many comparisons of the most widely used semiempirical models have been reported. They range from narrowly focused anecdotal discussions for specific molecules to detailed tests over large sets of molecules for performance in die calculation of various properties. We will discuss here a subset of these comparisons diat have the broadest impact - those looking for a more thorough overview are referred to the bibliography at the end of the chapter. 

Elements (number) Subset (number) MNDO AMI PM3 MNDO/d 

2 kcal moC, respectively, to 3.0, 2.3, and 2.2 kcal moC, respectively, when bond/group equivalents were used in place of atoms as the fundamental fragments. 

Correct molecular structures are dependent on the proper location of wells in the PES, so they are intimately related to the energetics of conformational analysis. For organic molecules, most gross structural details are modeled with a reasonable degree of accuracy. Dewar, Jie, and Yu (1993) evaluated AMI and PM3 for 344 bond lengths and 146 valence angles 

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GENERAL PERFORMANCE OVERVIEW OF BASIC NDDO MODELS... 

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