Electronic structure and molecular dynamics of breaking the RO–NO2 bond

Decomposition of energetic molecules such as pentaerythritol tetranitrate is accompanied by extensive changes in their electronic configuration and thus is challenging for ab initio Born-Oppenheimer molecular dynamics simulations. The performance of single-determinant methods (in particular, density-functional theory) is validated on electronic structure and molecular dynamics simulations of RO-NO(2) bond dissociation in a smaller nitric ester, ethyl nitrate. Accurate description of dissociating molecule requires using unrestricted, spin-symmetry-broken orbitals. However, the iterative self-consistent field procedure is prone to convergence failures in the bond-breaking region even if robust convergence algorithms are employed. As a result, molecular dynamics simulations of unimolecular decomposition need to be closely monitored and manually restarted to ensure seamless transition from the closed-shell to open-shell configuration.