RPA(D) and HRPA(D): Calculating NMR Spin–Spin Coupling Constants in Free Amino Acid Residues

In the pursuit of computational methods which boast both low computational cost and a high degree of accuracy, the SOPPA-derived methods RPA(D) and HRPA(D) are showing great promise. This study aims to further the benchmarking of these two methods in comparison with both the original SOPPA and the CCSD method by calculating NMR spin–spin coupling constants in the backbone structure of free amino acid residues. Based on a small basis set study, the relative performance of the methods was not found to be heavily dependent on the size of the basis set. While HRPA(D) was found to reproduce the SOPPA results to a consistently high degree of accuracy, RPA(D) reproduced the CCSD results for the one-bond coupling constants more accurately than both HRPA(D) and SOPPA.