Kazushi Fujimoto, Rajdeep Payal, Tomonari Hattori, Wataru Shinoda, Masayuki Nakagaki, Shigehiko Sakaki, and Susumu Okazaki
J. Comput. Chem., 40, 2571-2576 (2019).
A dissociative force eld for all-atomistic molecular dynamics calculations has been developed to investigate impact fracture of polymers accompanying dissociation of chemical bonds of polymer main chain. Energy of dimer molecules was evaluated as a function of both bond-length b and bond-angle by CASPT2 calculations whose quality is enough to describe dissociation of chemical bonds. Because we found that the bond dissociation energy D decreases with increasing bond-angle, we employed the Morse- type function VBond (b,θ) = {D-VAngle (θ)} [ 1 - exp{-α(b-b0)-β(b-b0)2}] where a quartic function VAngle (θ) = k1(θ-θ0) +k2(θ-θ0)2 +k3(θ-θ0)3 +k4(θ-θ0)4. This function reproduced well the CASPT2 potential energy surface in a wide range of b and θ. The parameters have been obtained for four popular glassy polymers, polyethylene, poly(methyl methacrylate), poly(styrene), and polycarbonate.