Automated potential energy surface development and quasi-classical dynamics for the F− + SiH3I system

We report a potential energy surface (PES) development for the F- + SiH3I system to study its gas-phase reactions through quasi-classical dynamics simulations. The PES is represented by a full-dimensional permutationally invariant polynomial fitted to composite coupled cluster energy points obtained at the ManyHF-[CCSD-F12b + BCCD(T) - BCCD]/aug-cc-pVTZ(-PP) level of theory. The development was automated by Robosurfer, which samples the configurational space, manages ab initio calculations, and iteratively extends the fitting set. When selecting the ab initio method, we address two types of electronic structure calculation issues: first, the gold standard CCSD(T)-F12b is prone to occasional breakdown due to the perturbative (T) contribution, whereas CCSD-F12b + BCCD(T) - BCCD, with the Brueckner (T) term, is more robust; second, the underlying Hartree-Fock calculation may not always converge to the global minimum, resulting in highly erroneous energies. To mitigate this, we employed ManyHF, configuring the Hartree-Fock calculations with multiple initial guess orbitals and selecting the solution with the lowest energy. According to the simulations, the title system exhibits exceptionally high and diverse reactivity. We observe two dominant product formations: SN2 and proton abstraction. Moreover, SiH2F- + HI, SiHFI- + H2, SiH2FI + H-, SiH2 + FHI-, SiH2 + HF + I-, and SiHF + H2 + I- formations are found at lower probabilities. We differentiated inversion and retention for SN2, both being significant throughout the entire collision energy range. Opacity- and excitation functions are reported, and the details of the atomistic dynamics are visually examined via trajectory animations.