On the choice of shape and size for truncated cluster-based x-ray spectral simulations of 2D materials

Abstract

Truncated cluster models represent an effective way for simulating X-ray spectra of 2D materials. Here we systematically assessed the influence of two key parameters, the cluster shape (honeycomb, rectangle, or parallelogram) and size, in X-ray photoelectron (XPS) and absorption (XAS) spectra simulations of three 2D materials at five K-edges (graphene, C 1s; C3N, C/N 1s; h-BN, B/N 1s) to pursue the accuracy limit of binding energy (BE) and spectral profile predictions. Several recent XPS experiments reported BEs with differences spanning 0.3, 1.5, 0.7, 0.3, and 0.3 eV, respectively. Our calculations favor the honeycomb model for stable accuracy and fast size convergence, and a honeycomb with ~10 nm side length (120 atoms) is enough to predict accurate 1s BEs for all 2D sheets. Compared to all these experiments, predicted BEs show absolute deviations as follows: 0.4-0.7, 0.0-1.0, 0.4-1.1, 0.6-0.9, and 0.1-0.4 eV. A mean absolute deviation of 0.3 eV was achieved if we compare only to the closest experiment. We found that the sensitivity of computed BEs to different model shapes depends on systems: graphene, sensitive; C3N, weak; h-BN, very weak. This can be attributed to their more or less delocalized π electrons in this series. For this reason, a larger cluster size is required for graphene than the other two to reproduce fine structures in XAS. The general profile of XAS shows weak dependence to model shape. Our calculations provide optimal parameters and accuracy estimations that are useful for X-ray spectral simulations of general graphene-like 2D materials.

First-principles simulation of X-ray spectra of graphdiyne and graphdiyne oxides at the carbon K-edge

“…And the IGLO-III basis set 48 and the DZVP basis set 55 were used for the excited atoms and the atoms of rest, respectively. Furthermore, the simulation was done in the gas phase while the experiment was carried out in the solid state and therefore the work function φ needs to be considered and subtracted to get the IPs in the solid phase, 30,39,56 IP solid = IP gas − φ .The work function of pure GDY was calculated at the size of 1 × 1 with the same conditions and yielded a value of 5.1 eV.…”

“…S3 (ESI †) was utilized due to its stable accuracy and fast size convergence. 39 NEXAFS spectra were computed at the DFT level with the equivalent core hole (ECH, also known as Z + 1) approximation. [40][41][42] This method has shown good performance in a wide range of carbon materials, including ideal, N and B-N doped graphene, [43][44][45] and heteroatom-doped graphynes.…”

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

“…One has to define proper cluster size to balance between accuracy and efficiency. In practice, large system size can sometimes make the self-consistent field (SCF) calculation with a core hole difficult. , …”

“…In practice, large system size can sometimes make the self-consistent field (SCF) calculation with a core hole difficult. 23,24 Hybrid methods provide more efficient solutions for large systems than pure cluster-based calculations. They are especially suitable for X-ray spectral simulations due to the locality of core excitations.…”

Global Impact and Balancing Act: Deciphering the Effect of Fluorination on B 1s Binding Energies in Fluorinated h-BN Nanosheets

“…The two representative observations show conflicts. As we know, existing XPS data suffer from inconsistency due to different calibration procedures used. , Is this conflict a simple calibration problem, or is there any deeper physical/chemical insight behind it? Further, in comparison to pure h -BN, why does fluorination sometimes lead to a blue (as in ref ) and sometimes a red (as in ref ) shift?…”