Symmetrized systematic molecular fragmentation model and its application for molecular properties

A novel molecular fragmentation method is proposed, which is based on the Systematic Molecular Fragmentation (SMF) model of Collins [Phys. Chem. Chem. Phys. 21, 7744 (2012)]. In comparison to the original SMF model, which produces large fragments for branched molecules, sizes of fragments in the new scheme correspond exactly to the requested fragmentation level, which in turn allows for cheaper calculations at advanced electron-correlated levels of theory. Additionally, the new approach treats a local bonding pattern around branching points in a symmetric way at cost of the introduction of fractional weights for some fragments. Numerical tests of the new method, denoted as Symmetrized SMF, show that already the third level of fragmentation reproduces molecular energies and dipole moments accurately enough for tested molecules. A hybrid model for the SSMF with conjunction of the Hartree–Fock and Møller-Plesset theories has been proposed, where the nonbonding interactions are calculated with Symmetry-Adapted Perturbation Theory.