Performance of the TPSS Functional on Predicting Core Level Binding Energies of Main Group Elements Containing Molecules: A Good Choice for Molecules Adsorbed on Metal Surfaces

Abstract

Here we explored the performance of Hartree-Fock (HF), Perdew-Burke-Ernzerhof (PBE), and Tao-Perdew-Staroverov-Scuseria (TPSS) functionals in predicting core level 1s binding energies (BEs) and BE shifts (ΔBEs) for a large set of 68 molecules containing a wide variety of functional groups for main group elements B → F and considering up to 185 core levels. A statistical analysis comparing with X-ray photoelectron spectroscopy (XPS) experiments shows that BEs estimations are very accurate, TPSS exhibiting the best performance. Considering ΔBEs, the three methods yield very similar and excellent results, with mean absolute deviations of ∼0.25 eV. When considering relativistic effects, BEs deviations drop approaching experimental values. So, the largest mean percentage deviation is of 0.25% only. Linear trends among experimental and estimated values have been found, gaining offsets with respect to ideality. By adding relativistic effects to offsets, HF and TPSS methods underestimate experimental values by solely 0.11 and 0.05 eV, respectively, well within XPS chemical precision. TPSS is posed as an excellent choice for the characterization, by XPS, of molecules on metal solid substrates, given its suitability in describing metal substrates bonds and atomic and/or molecular orbitals.

Predicting core level binding energies shifts: Suitability of the projector augmented wave approach as implemented in VASP

“…As found for FS n , the half excited electron screening was responsible of an average increase of errors in ΔBEs of 0.53 and 0.8 eV for PBE and TPSS, respectively. More importantly, the ΔBEs MAE at PBE and TPSS levels of 0.37 and 0.21 eV are of the same accuracy of corresponding relativistic ΔSCF calculations of 0.24 and 0.25 eV as obtained in an earlier work . Hence, for gas phase molecules, the JS n method in combination with a PAW core description is capable to reach the same high degree of accuracy for ΔBEs than all electron ΔSCF using a fully uncontracted near HF limit basis set .…”

“…However, computed ΔBEs estimates, that is, relative BE shifts, line up well with experimental trends. For the PBE and TPSS exchange‐correlation functionals, ΔBE estimates using the JS n approach yield MAEs of only 0.37 and 0.21 eV, respectively, and are thus of similar size to all electron ΔSCF calculations with saturated basis sets, thereby approaching the experimental accuracy of HR‐XPS of 0.1 eV. The accuracy of the JS n approach is useful not only for molecules but also promises its use in assigning ΔBEs of molecular moieties on material surfaces, with concomitant applications in surface science, nanotechnology, and heterogeneous catalysis, although its accuracy in such systems remains to be confirmed.…”

“…The BE values obtained through the ΔSCF approach include final state (FS) effects—that is, the excited core electron is removed from the system under scrutiny and the electronic structure modified according to the electron hole. Indeed, by considering the electronic screening of the core state and relativistic effects, one can obtain BE estimates well within the XPS experimental accuracy of 0.1 eV, either based on Hartree–Fock (HF) calculations, or using methods within DFT . Such a high level of accuracy for isolated molecules would be desirable when they are adsorbed to a solid surface, to distinguish among different molecular adsorption conformations, as well as to monitor heterogeneously catalyzed processes.…”

“…Only these functionals have been assessed, as the ultimate goal is to use them to assign XPS features of atoms and/or molecules in different positions and/or conformations on TM supports. The ΔSCF calculations for this large set of molecules have been previously carried out using a full all electron description and a near HF limit basis set, obtained within spin restricted open‐shell formalisms for both HF and KS methods …”

“…To address the accuracy of the these procedures above described, here we take advantage of the recent evaluation of PBE and TPSS performance on estimating DSCF BEs and DBEs for 1s CL for a large dataset of 68 molecules containing a wide variety of functional groups for first row main group elements B!F, considering up to 185 CLs, for which accurate gas phase experimental BEs are known, see Table S1 in Supporting Information. [9,[29][30][31][32] Only these functionals have been assessed, as the ultimate goal is to use them to assign XPS features of atoms and/or molecules in different positions and/or conformations on TM supports. The DSCF calculations for this large set of molecules have been previously carried out using a full all electron description and a near HF limit basis set, obtained within spin restricted open-shell formalisms for both HF and KS methods.…”