A Brand New Reactive Potential Made Molecular Dynamics on Chemical Reaction Possible

A new idea is brought in this paper that molecular dynamics with a force field integrated a brand new reactive potential form which considered bond breaking and forming can be used to simulate chemical reaction. As an example, we report here a force field CRACK developed for studying pyrolysis process of n-alkane. CRACK splines together a harmonic well and a shallow Lennard-Jones well: the harmonic well models C-C covalent bond while the Lennard-Jones well models long-range van der Waals forces. These two wells are separated by an energy barrier which controls dissociation and recombination. To validate this new reactive potential form, CRACK has been used to simulate pyrolysis process of n-decane and n-octane by molecular dynamics (MD). The dissociation probabilities as well as product distributions were analyzed and the time history of pyrolysis was illustrated. The research on dissociation probabilities shows that the defined pyrolytic temperature could be altered by changing the displacement constant de which controls the height of dissociation barrier of C-C bond and it was also found that the pyrolytic temperature of n-octane was higher than of n-decane at the same de, which is consistent with the pyrolysis fundamental. The time history of decane pyrolysis revealed an inspirer result that CRACK force field certainly reflected the recombination between free radicals. Another exciting result is that, by analysis of the distribution of pyrolytic products, the main products distribution was observed to transfer from mid-short to mid-long chains and chain distribution tended to shorter or longer with the elevated temperature which is well consistent with the regularity of thermal cracking. We announce that molecular dynamics can be certainly used to simulate the process of chemical reaction as long as reactive potential is proper.