Modification of the potential surface by an applied force

2 Stretching small molecules using density functional theory 

Beyer applied a similar approach but using first principles DFT calculations to examine the rupture of small molecules. The objective was to characterize the rupture of specific bonds and compare the rupture forces. This approach, in which the molecular configuration is stretched along a specific direction was described as Constrained Geometries simulate External Force and determines the energy as a function of the extension 

The results from these calculations are then compared with experiment by considering the bond rupture probability density as a function of force 

The same principle was applied to investigating reaction mechanisms in which a strained bond is attacked, causing rupture in a reaction with the attacking species. This type of reaction is, however, difficult to assess using static calculations as the reaction itself cannot be followed and only one line of approach of a neighboring molecule is assessed. 

Hanson and Martin applied the same approach to investigate the rupture of isoprene and butadiene oligomers in order to investigate covalent bond rupture in rubber.Using density functional theory, they identified the point of rupture where the unrestricted solution to the Kohn-Sham electronic wave functions falls below the restricted solution. This implies that the rupture process should be heterolytic and so this concept can only be applied for instances in which radical species are formed in the initial rupture event. 

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