Molecular conformation global minimum

The most serious problem with MM as a method to predict molecular structure is convergence to a false, rather than the global minimum in the Born-Oppenheimer surface. The mathematical problem is essentially still unsolved, but several conformational searching methods for approaching the global minimum, and based on either systematic or random searches have been developed. These searches work well for small to medium-sized molecules. The most popular of these techniques that simulates excitation to surmount potential barriers, has become known as Molecular Dynamics [112]. 

Fig. 23 Overlay of selected conformers of laulimalide within 2 kcal mol-1 of the global minimum determined from molecular modeling and NMR data in CD3OD solution. These low-energy conformations closely resemble the X-ray conformation. (Reprinted with permission from [134]. Copyright 2005 Elsevier)...

Nowek and Leszczynski used ab initio post-Hartree-Fock and DFT B3LYP calculations to resolve the problem of the structure of the Ge- OH2 complex274. The molecular geometries of the nonplanar 17 (Ci) and planar 18 (Cs) conformers were optimized at the DFT and MP2 levels of theory using TZP and TZ2P basis sets. The nonplanar complex 17 with a Ge - O distance of 2.214 A (MP2), 2.268 A (B3LYP) corresponds to a global minimum while complex 18 was found to be very weakly bound (if bound at all). 

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