Complex sentence: It is essentially a more efficient method of finding reasonable approximations of molecular orbitals, useful in predicting physical and chemical nature of the molecule under study since molecular orbital characteristics have implications with regards to both the basic structure and reactivity of a molecule.
Split into simpler sentences: It is essentially a more efficient method for coming up with reasonable approximations of molecular orbitals. Molecular orbital characteristics have implications with regards to both the basic structure and reactivity of a molecule.