On the Choice of the Optimal Functional Dependence of Magnetic Shielding on the 27Al Nucleus on the Si–O–Al Angles in HBEA, HGOO, and HFER Zeolites

Magnetic shielding σ of 27Al nuclei in the crystallographic T-positions of polymorph B of zeolite HBEA with a ratio of Si/Al = 31, as well as of zeolites HGOO (Si/Al = 15) and HFER (Si/Al = 35), was estimated based on quantum-chemical calculations with periodic boundary conditions (PBCs) using the density functional theory (DFT) method with the PBE functional, including the dispersion energy. Approximation of the shielding σ(27Al) for three dehydrated zeolites is compared with respect to the angle ϑ = 〈Si–O–Al〉 and the functions cos(ϑ)/(cos(ϑ) – 1), cos(ϑ), and sin(ϑ) presented in the literature. The most suitable function for semiquantitative estimation of screening and chemical shifts was chosen based on the analysis.