CORRELATED AND GAUGE ORIGIN INDEPENDENT CALCULATIONS OF MAGNETIC-PROPERTIES .2. SHIELDING CONSTANTS OF SIMPLE SINGLY BONDED MOLECULES

We have applied a gauge origin invariant method for calculations of nu clear magnetic shielding constants to the singly bonded molecules BF, F2, BH3, CH4, NH3, H2O, and HF as well as to the H-1 shielding constan ts of HCN and C2H2. The calculations were performed at the RPA and sec ond order polarization propagator (SOPPA) level of theory. For most mo lecules the correlation contribution in SOPPA is less diamagnetic than in the comparable MP2 calculations. For F2, SOPPA gives a large param agnetic correlation correction whereas the MP2 method gives a very sma ll correlation contribution. For all molecules agreement with experime ntal results is generally improved at the SOPPA level compared to RPA. We have also demonstrated that second order gauge origin invariant, c ommon and local origin (SOLO) methods do not necessarily give the same shielding even in the limit of a converged basis set.