Figure 1. Optimized geometry of the truncated Zn-MOF
(BP86/def2-TZVPP).
The first step consisted in optimizing the Zn-MOF as well as the
interacting system Zn-MOF-analyte with the ORCA package.40 All structures were optimized via the
gradient-corrected Becke–Perdew (BP86)41exchange-correlation functional using the triple-zeta valence with two
sets of polarization functions (def2-TZVPP) 42 basis
set. In the second stage of this work, we performed a study of the
optical properties of the Zn-MOF and Zn-MOF-analyte systems by means of
the Time-dependent Density Functional Theory (TD-DFT) approach. To
simulate the vertical transitions, 50 excitations were computed at the
hybrid exchange-correlation functional (B3LYP) 43 as
well as the Coulomb Attenuated Method (functional, CAM-B3LYP)44 and def2-TZVPP basis set. Finally, we analyzed the
nature of the interaction Zn-MOF-analyte based on the energy
decomposition analysis (EDA) proposed by
Morokuma–Ziegler.45 The interaction energy
(ΔEint) between two defined fragments according to the
EDA scheme can be divided into four components:
ΔEint = ΔEElec + ΔEPauli+ ΔEOrb + ΔEDisp (1)
Where ΔEElec accounts for the classical electrostatic
interaction between the fragments as they are brought to their positions
in the final structure. The second term ΔEPauli is
related to the repulsive interaction of Pauli, between occupied orbitals
of both molecular fragments. The third term ΔEOrbexpresses the possible interactions between molecular orbitals related
to the charge transfer, polarization, etc. This term can be analyzed by
the natural orbital of chemical valence method proposed by
Mitoraj.46-47 The term ΔEDispdescribes the dispersion forces acting between the fragments. We
consider the long-range interactions, using Grimme’s D3 dispersion
correction for EDA calculations.48