Quantum mechanics capacitance molecular mechanics modeling of core-electron binding energies of methanol and methyl nitrite on Ag(111) surface

Abstract

We study a newly devised quantum mechanics capacitance molecular mechanics (QMCMM) method for the calculation of core-electron binding energies in the case of molecules adsorbed on metal surfaces. This yet untested methodology is applied to systems with monolayer of methanol/methyl nitrite on an Ag(111) surface at 100 K temperature. It was found out that the studied C, N, and O 1s core-hole energies converge very slowly as a function of the radius of the metallic cluster, which was ascribed to build up of positive charge on the edge of the Ag slab. Further analysis revealed that an extrapolation process can be used to obtain binding energies that deviated less than 0.5 eV against experiments, except in the case of methanol O 1s where the difference was as large as 1.8 eV. Additional QM-cluster calculations suggest that the latter error can be connected to the lack of charge transfer over the QM-CMM boundary. Thus, the results indicate that the QMCMM and QM-cluster methods can complement each other in a holistic picture of molecule-adsorbate core-ionization studies, where all types of intermolecular interactions are considered.

Polarizable QM/MM Approach with Fluctuating Charges and Fluctuating Dipoles: The QM/FQFμ Model

“…38−41 The heterogeneous environment is instead modeled in terms of nonpolarizable force fields. 38 QM/FQFμ is not limited to any specific kind of environment (pending an accurate parametrization is obtained), thus being of broader applicability with respect to other approaches.…”

“…In addition, differently from DIM and CMM, FQFμ has been formulated in terms of a variational functional (see eqs and ), which guarantees its rigorous further extension to molecular properties . It is worth remarking that the application of both QM/DIM and QM/CMM has been so far limited to the study of molecular properties of systems adsorbed on a metal surface, in which the metal surface is described by DIM or CMM force fields. − The heterogeneous environment is instead modeled in terms of nonpolarizable force fields . QM/FQFμ is not limited to any specific kind of environment (pending an accurate parametrization is obtained), thus being of broader applicability with respect to other approaches.…”

A QM/MM Study on the X-ray Spectra of Organic Proton Transfer Crystals of Isonicotinamides

“…The usage of point charges at relatively distant atoms provides a more accurate description of the electrostatic effect than the supermolecule-continuum model. Applications in XPS/XAS spectral simulations cover a wide range of systems, including organic crystals, metallic oxides, metalloenzymes, , surface adsorbates, gas phase polymers, and solutions. − For example, Scanlon et al simulated the Ti L 3 edge XPS spectra of TiO 2 by combining DFT with a polarizable force field, which helped understand the charge carrier separation between the rutile and anatase phases. Neese and co-workers used time-dependent DFT (TDDFT)/MM to study the Fe K-edge XAS spectra of a metalloenzyme, which helped understand its catalytic reaction.…”

“…Neese and co-workers used time-dependent DFT (TDDFT)/MM to study the Fe K-edge XAS spectra of a metalloenzyme, which helped understand its catalytic reaction. Ågren and co-workers applied DFT/MM to calculate the K-edge XPS or BE of polymers and ethanol and glycine in water solutions, and they also applied the so-called quantum mechanics capacitance molecular mechanics (QMCMM) method for a monolayer of small organic molecules absorbed on the Ag(111) surface …”

“…Ågren and co-workers applied DFT/MM to calculate the K-edge XPS or BE of polymers 31 and ethanol 33 and glycine 32 in water solutions, and they also applied the so-called quantum mechanics capacitance molecular mechanics (QMCMM) method for a monolayer of small organic molecules absorbed on the Ag(111) surface. 30 Proton transfer crystals have more structural complexities than molecular crystals with pure neutral residues. Proton transfer leads to localized charges.…”