Periodic DFT computation of rotational barriers for linear molecules in zeolites: Validation via zero-point energies and isotopic heat difference values of adsorbed H2/D2

• Published in: Materials chemistry and physics Vol. 294; p. 126929
• Main Authors: Rybakov, A.A., Trubnikov, D.N., Vercauteren, D.P., Larin, A.V.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2023
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2022.126929

A climbing image nudged elastic band (cNEB) algorithm was applied on the basis of density functional theory (DFT) calculations of the rotational barriers of eight linear molecules (H2, N2, O2, CO, CO2, NO, N2O, C2H2) adsorbed in NaY and NaCaY periodic zeolite models at the MeII cation sites (the Na or Ca metal cation in the SII site) located near the 6R windows. A specific approach is applied for molecules with positive quadrupole (H2, C2H2) and small negative quadrupole (3O2) moments while applying cNEB. The obtained T-geometry relative to the cation is the most frequent case for H2 adsorption in cationic form sieves and metalorganic frameworks (MOFs). The computed barriers for the T- and other linear (L) orientations are in good correlation with the quadrupole moments taken from literature irrespective of the dipole values (CO, NO, N2O). In the case of NaY, the Al distribution per 6R sites is also discussed which allowed finding particular favorite adsorption sites. The calculated zero-point energies relative to the obtained rotational barriers regarding the H2 - D2 pair result in a qualitative agreement with the experimental isotopic difference in the H2/D2 adsorption heats in NaY which ultimately lead to the H2/D2 separation coefficient. [Display omitted] Agreement with experimental differences of heats of adsorption of D2 and H2 is shown. Method to calculate the barriers for H2/D2 rotation in MeY is given with cNEB + VASP. Al distribution in NaY windows is confirmed basing on GGA and hybrid DFT schemes. Quadrupole defines rotational barrier of 8 gases near Me = Na and Ca cations in MeY. CO, NO, N2O dipoles have poor influence on rotational barrier near divalent cation.