The use of locally dense basis sets in correlated NMR chemical shielding calculations

Locally dense basis sets employ large sets of functions on a particular atom or small molecular region, and smaller or attenuated sets elsewhere. This approach has been shown to be very useful in calculating NMR chemical shieldings at the Hartree-Fock level on systems otherwise computationally expensive. In the present work it is shown that such mixed basis sets can also be successfully employed at the second order many-body perturbation theory level (MBPT[2], or MP2). Shielding calculations have been carried out on a variety of carbon-, nitrogen-, oxygen-, and phosphorus-containing molecules and the locally dense shielding results analyzed at Hartree-Fock and MP2 levels, and with our recently introduced estimated infinite order Moller-Plesset (EMPI) approach.