NMR espectroscopic parameters of HX and Si (Sn)X4 (X = H, F, Cl, Br and I) and SnBr4−nIn model compounds

► In this article we show a procedure to get accurate NMR σRef of Si and Sn. ► Calculations of σ on more than three heavy-atom-containing molecules are given. ► Our results are closer to δexp than previous calculations for SnX4 (X = H, Cl, Br, I). ► Optimized basis sets were considered for full R and NR calculations of NMR J and σ. ► Relativistic effects enlarge electron correlation effects on J-couplings.