Note on hydrogenic atomic orbitals to evaluate sensitive properties of molecules: An example of NMR chemical shifts

Now that the problems surrounding ab initio calculations over a Slater Type Orbital basis have been solved, it is available in several software packages. For general structures the STOP package (Slater Type Orbital Package) has offered ab initio SCF molecular properties since 1996, the requisite integrals all being evaluated analytically, including the four center term available since 1994. SMILES (Slater Molecular Integrals for Large Electronic Systems) has offered various basis sets, geometry optimization and CI since 2001. For density functional work, ADF, the Amsterdam Density Functional suite of programs, is a project dating from the 1970s with a 2003 edition. In this work the preferred ETOs (Exponential Type Orbitals) will be shown to be the hydrogenic orbitals and similar Coulomb Sturmians. Slater Type Functions (STFs) will be compared to them and suitable equivalent combinations, which are rarely used, given. The correct shielding of the nucleus, resulting from radial factors of hydrogenic orbitals is shown to be essential in the evaluation of precise nuclear shielding tensors for NMR spectroscopy of molecules using ab initio or DFT methods. The case study of benzothiazoles using natural abundance N-15 is re-examined and compared with previous work including measurements.