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Figure 4 (a) Net magnetic moment of iron as a function of total atom number in clusters; (b) the cohesive energy of iron carbide clusters as a function of total atom number in clusters. The decrease of the ratio of Fe/C (from Fe,C to Fe3C to Fe,C, to Fe,C) can induce the electron loss of iron on both bulk and clusters. Besides the Fe/C ratio, the size effect also plays an important role on charge transfer. From Figure 3d, one can find that larger clusters, more electrons transfer from iron to carbon, that is, more positive on iron and more negative on carbon. For instance, for Feg,C, (n = 1 ~ 5) clusters, the average Bader charges of iron atom changes

Figure 4 (a) Net magnetic moment of iron as a function of total atom number in clusters; (b) the cohesive energy of iron carbide clusters as a function of total atom number in clusters. The decrease of the ratio of Fe/C (from Fe,C to Fe3C to Fe,C, to Fe,C) can induce the electron loss of iron on both bulk and clusters. Besides the Fe/C ratio, the size effect also plays an important role on charge transfer. From Figure 3d, one can find that larger clusters, more electrons transfer from iron to carbon, that is, more positive on iron and more negative on carbon. For instance, for Feg,C, (n = 1 ~ 5) clusters, the average Bader charges of iron atom changes

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This article can be cited before page numbers have been issued, to do this please use: L. Zheng, X. Liu, Y. Meng, Y. Zhou, W. Guo, Q. Peng, Y. Yang, H. Jiao, Y. Liand X. Wen, Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/C6CP06224E.
This article can be cited before page numbers have been issued, to do this please use: L. Zheng, X. Liu, Y. Meng, Y. Zhou, W. Guo, Q. Peng, Y. Yang, H. Jiao, Y. Liand X. Wen, Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/C6CP06224E.
The Fe,,C, and Fe3,C, clusters (n = 1 ~ 7) as well as the Fes,Co, and Fe,g,C, (n 1 ~ 5) clusters, in which the stoichiometry is most relevant in the Fischer-Tropsch synthesis (which can be called “FTS-ratio” clusters) and carbon nanotube synthesis, are also predicted by RBPM (Figure 2). Figure 2. The geometrical configurations and the relative energies (eV) of the most stable FTS-ratio clusters corresponding to different carbon distributions. Olive for carbon atoms; Orange for iron atoms.
The Fe,,C, and Fe3,C, clusters (n = 1 ~ 7) as well as the Fes,Co, and Fe,g,C, (n 1 ~ 5) clusters, in which the stoichiometry is most relevant in the Fischer-Tropsch synthesis (which can be called “FTS-ratio” clusters) and carbon nanotube synthesis, are also predicted by RBPM (Figure 2). Figure 2. The geometrical configurations and the relative energies (eV) of the most stable FTS-ratio clusters corresponding to different carbon distributions. Olive for carbon atoms; Orange for iron atoms.
Figure 1. The most stable structures of Fe,C, (x < 8; y < 8) obtained by “random- bonding plus minimization”. Olive for carbon atoms; Orange for iron atoms.
Figure 1. The most stable structures of Fe,C, (x < 8; y < 8) obtained by “random- bonding plus minimization”. Olive for carbon atoms; Orange for iron atoms.
Figure 3. (a) The searched ground structures of Fe,C, with rich carbon obtained by RBPM. Olive for carbon atoms; Orange for iron atoms. (b) The density of states of Fes,Con (n = 1 ~ 5), as well as of FesC,(111) surface. (c) The average bond length of Fe-Fe, Fe-C, and C-C as a function of total atom number. (d) The average Bader charge of iron, carbon as a function of total atom number.
Figure 3. (a) The searched ground structures of Fe,C, with rich carbon obtained by RBPM. Olive for carbon atoms; Orange for iron atoms. (b) The density of states of Fes,Con (n = 1 ~ 5), as well as of FesC,(111) surface. (c) The average bond length of Fe-Fe, Fe-C, and C-C as a function of total atom number. (d) The average Bader charge of iron, carbon as a function of total atom number.
‘9T9G:ST 9LOZ/TTAT Uo Arerqry uebipy jo Asta Aq papeotuMmod ‘9T0Z JEqUIBAON OT UO peysyqnd *The bonding symbols 1F-6F/number refers to the number of bonds formed between the adsorbing CO molecule and the Fe surface atoms and the average Fe-CO bond length (A). Table 1. The most stable adsorption type of CO on the surfaces of FesC2 and clusters.
‘9T9G:ST 9LOZ/TTAT Uo Arerqry uebipy jo Asta Aq papeotuMmod ‘9T0Z JEqUIBAON OT UO peysyqnd *The bonding symbols 1F-6F/number refers to the number of bonds formed between the adsorbing CO molecule and the Fe surface atoms and the average Fe-CO bond length (A). Table 1. The most stable adsorption type of CO on the surfaces of FesC2 and clusters.
Figure 5. (a) The critical carbon chemical potential in mixed CO/CO, for iron carbide clusters (dotted lines) and bulks (solid lines); (b) The component matrix of iron carbide clusters under different carbon chemical potential corresponding to a.
Figure 5. (a) The critical carbon chemical potential in mixed CO/CO, for iron carbide clusters (dotted lines) and bulks (solid lines); (b) The component matrix of iron carbide clusters under different carbon chemical potential corresponding to a.
Figure 6. (a) The advanced frontier energy level interactions pattern between CO and iron carbide clusters which are computed from VASP (red for occupied energy levels; blue for unoccupied ones); (b) The Bader charge of Fe;C, clusters with without CO (top) and with CO (bottom). Olive for carbon atoms; Orange for iron atoms. One also can learn the adsorption behaviour from the molecule orbital side. Figure 6a shows the advanced frontier interaction between CO and iron carbide clusters computed from VASP code. As expected, there are more discrete states in the small clusters. The process 1 (iron donating process), which stands for 2m* unoccupied orbital of CO interacting with the HOMO of clusters, can result in electron transportation from cluster to CO, while the process 2 (iron accepting process) can do the opposite influence. As shown in Figure 6b, when iron atoms bond to CO, the iron atoms loss about 0.2 e leading to more positive charge. Therefore, the process 1 in Figure 6a is the predominant reason for the adsorption of CO on iron carbide clusters. Obviously, from molecular orbital point of view, the large energy level gap makes the process 2 a weak interaction. As size growth of cluster for Fe,C, to Fe25Ci9 does little changes in the HOMO and LUMO, the size effect has limited influence in their adsorption pattern. The finding provides a way to tune the
Figure 6. (a) The advanced frontier energy level interactions pattern between CO and iron carbide clusters which are computed from VASP (red for occupied energy levels; blue for unoccupied ones); (b) The Bader charge of Fe;C, clusters with without CO (top) and with CO (bottom). Olive for carbon atoms; Orange for iron atoms. One also can learn the adsorption behaviour from the molecule orbital side. Figure 6a shows the advanced frontier interaction between CO and iron carbide clusters computed from VASP code. As expected, there are more discrete states in the small clusters. The process 1 (iron donating process), which stands for 2m* unoccupied orbital of CO interacting with the HOMO of clusters, can result in electron transportation from cluster to CO, while the process 2 (iron accepting process) can do the opposite influence. As shown in Figure 6b, when iron atoms bond to CO, the iron atoms loss about 0.2 e leading to more positive charge. Therefore, the process 1 in Figure 6a is the predominant reason for the adsorption of CO on iron carbide clusters. Obviously, from molecular orbital point of view, the large energy level gap makes the process 2 a weak interaction. As size growth of cluster for Fe,C, to Fe25Ci9 does little changes in the HOMO and LUMO, the size effect has limited influence in their adsorption pattern. The finding provides a way to tune the
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DFT calculationiron carbide
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