## 5 Simulations  
C\({}_{5}\)F\({}_{10}\)O and Cu reacted at the gas-solid interface. To further understand the interaction mechanism between C\({}_{5}\)F\({}_{10}\)O and Cu, a theoretical calculation was performed based on density functional theory (DFT) by using the DMol\({}^{3}\) module of Materials Studio [26; 27]. The Dmol\({}^{3}\) module is a unique DFT quantum mechanics software that can study gas phase, solution, surface, and solid systems. Furthermore, the Dmol\({}^{3}\) module is the fastest in molecular density functional calculation, which can quickly optimize the structure of molecules and solid systems, saving calculation time and other advantages. Copper clusters have many isomers, and the number of isomers rapidly increases along with the number of atoms in the cluster. Cu\({}_{13}\) clusters were selected for the calculation. According to previous studies [28; 29; 30], the icosahedron structure that comprises 13 copper atoms is considered the most stable (Figure 8a). In this structure, 12 copper atoms form an icosahedral shell and the most stable Cu\({}_{13}\) nanoclusters with a core copper atom. The copper atoms on the outer shell have a coordination number of six. Therefore, the Cu\({}_{13}\) nanocluster only has three adsorption sites, namely top, bridge, and Hcp (Figure 8b). Generalized gradient approximation with the Perdew-Burke-Ernzerhof function was employed to calculate the electronic exchange correlation, and the double numerical plus basis set with a polarization d-function was used to expand the valence electron functions. The smearing value was set as 0.005 Ha. To determine the accurate activation barrier of the Cu and C\({}_{5}\)F\({}_{10}\)O reaction, the complete linear synchronous transit and quadratic synchronous transit (LST/QST) approach was used to search for the transition state of the Cu and C\({}_{5}\)F\({}_{10}\)O reaction [31; 32]. The molecular structure of C\({}_{5}\)F\({}_{10}\)O suggests that C\({}_{5}\)F\({}_{10}\)O has three adsorption sites, namely O, F, and F\({}_{3}\) (Figure 8a). Therefore, the C\({}_{5}\)F\({}_{10}\)O and Cu\({}_{13}\) nanoclusters have nine adsorption modes, and the calculation results are shown in Figure 8c-e.  
Figure 8: _Cont_. Before the calculation, the target atom in C\({}_{5}\)F\({}_{10}\)O was given a distance from the Cu\({}_{13}\) nanocluster core-shell structure, and then the intermolecular adsorption was calculated. Figure 8c shows that the F in Figure 8a can react with the Cu\({}_{13}\) nanocluster at the bridge and Hcp adsorption sites of the Cu\({}_{13}\) nanocluster to form a chemical bond with the Cu nanocluster, thereby resulting in the cleavage of the C-F bond of the alpha (\(\alpha\)) carbon atom. At the same time, given the close position of the upper F and O atoms in the C\({}_{5}\)F\({}_{10}\)O molecular space structure, when the distance between the F atom and the Cu\({}_{13}\) nanocluster is small, the distance between the O atom and Cu\({}_{13}\) nanocluster is also small. The chemical nature of the carbonyl group is relatively active. In the chemical reaction, the C=O double bond is easily broken. Therefore, O reacts with the Cu nanocluster to break the C=O double bond and to form a Cu-O metal ion bond. The carbon of the carbonyl group combines with the carbon atom at the alpha position to form a carbon-carbon double bond (Figure 8e). At the top adsorption site, only one Cu atom in the Cu\({}_{13}\) nanocluster is located close to the C\({}_{5}\)F\({}_{10}\)O molecule, and F cannot form a chemical bond with the Cu nanocluster. The calculations reveal that only the carbonyl group reacts with Cu to break the carbon-oxygen double bond into a single bond and that the F atom on the \(\alpha\)-position carbon atom can react with the Cu nanocluster to break the fluorocarbon bond at the \(\alpha\)-position carbon atom and form a carbon-carbon double bond.