Computational Chemistry: Beyond the BlackBox Approach

Modern computer hardware and efficient software development have made computational chemistry an essential component of the chemist’s toolkit. Many of the black box approaches in wide use today, when applied properly, provide useful spectroscopic, geometrical, and qualitative energetic information about the system(s) of interest. Further information can be gained, however, from using higher level theoretical methods and providing a more thorough analysis of electronic wavefunctions.

This talk will discuss the application of high-level computational techniques to several different interesting chemical systems. In the first portion of the talk, the application of multi-reference Møller-Plesset perturbation theory of the second order (MRMP2) to systems containing the non-innocent pyridine-2,6-diimine (PDI) ligand will be discussed. It will be shown that we can provide a better energetic description of these systems, and that in certain cases our multi-reference approach is necessary to properly describe the wavefunction. In the second portion of the talk, the electronic structure and energetics of some new benzene dimers will be analyzed with MRMP2. The MRMP2 results are also compared with a number of other theoretical methods, including another multi-reference perturbative approach termed N-electron valence perturbation theory (NEVPT2). Surprisingly, the NEVPT2 results diverge from the MRMP2 results presumably due to the strong internal contraction employed in the implementation of NEVPT2. Thirdly, the record ⁷Li NMR chemical shift recently reported (δ = -23.9 ppm) for a Li⁺ sandwiched between two five-membered rings in corannulene will be analyzed via the canonical molecular orbitals.