I've been playing around with WebMO and Gaussian for the past couple weeks, and I have come across the term NBO. What is the difference between Molecular orbitals and Natural Bond orbitals? Is there a reason you'd use one over the other? Are both publishable? Is one easier to calculate? For the record, I am interested in Ti/Ta/W complexes of N-O and C based polydentate ligands, if that makes a difference.