求助：为什么模仿一篇FeCo双金属单原子论文计算差分电荷密度时趋势与原文不一致

ComputationPawn

我使用的是2019版本MS软件中的CASTEP模块，在模仿《Bi-functional electrocatalysis through synergetic coupling strategy of atomically dispersed Fe and Co active sites anchored on 3D nitrogen doped carbon sheets for Zn-air battery》这篇论文进行差分电荷密度进行计算时，出现了以下问题：

（1）所计算的Fe-N4，Co-N4，Co-Fe-N4构型的差分电荷密度的Display style的value值为0.005（原文是0.01），另外配色方案与默认几乎相反；
（2）我自己计算的Fe-N4构型的差分电荷密度在选用上述value值及配色方案后，与原文基本一致；但是Co-Fe-N4的差分电荷密度与原文趋势不同，如下图原文中“Co原子引入后，Fe位点的蓝色区域减小”，我自己算的“Co和Fe两个原子各作为一个Set，计算差分电荷密度后，相较于Fe-N4及Co-N4，Fe位点的差分电荷密度无明显变化，而Co位点的蓝色区域减小。”
（3）Co-N4的差分电荷密度是我自己算的，原文只给了Fe-N4和Co-Fe-N4的电荷差分电荷密度。

想问大家的是，这种差异可能是由于什么参数导致的？

文中对于差分电荷密度的描述：The density functional theory (DFT) calculation studies were performed to explore the role of Co dopants and the synergistic effect between FeN4 and CoN4 for ORR [45–47]. The computational details are presented in Supporting Information and structure models were established (Fig. 6a). The A-FeCo@NCNs was used to study the effect of Co atom dopants in FeN4. In comparison, A-Fe@NCNs is obtained without introducing Co element and A-FeCo-NP@NCNs is built with Co metallic nanoparticles adjacent to FeN4. The differential charge density distributions of those structural models are showed in Figs. 6b and S13. Moreover, the Bader charge for metal atoms in FeN4, FeN4-CoN4, and FeN4-Co structures (Fig. S14) was obtained. Of note, the metal atoms (both Fe and Co) are electron donors, while the adjacent C/N atoms are electron acceptors. Fe atom in FeN4 loses 1.052 electrons, while Fe atom in FeN4-CoN4 loses 1.048 electrons, which indicates the increased electron density around Fe atom in FeN4-CoN4, agreeing well with the XPS results [48,49]. It is known that that higher electron density would be favorable for the adsorption and activation of O2 molecules and the high ORR activities of Fe single atom catalysts are mainly contributed by the enhanced electron density around Fe atoms [50]. Based on these results, it can be deduced that Fe and Co in the carbon framework will affect each electronic structure. Moreover, such synergetic effect will improve the activity towards ORR.


以下是我计算过程中参数的设置：
注：
1）本人所算电荷为Mulliken电荷，未转换为与文中一致的Barder电荷；
2）差分电荷密度的Isosurface中的Value值及配色方案均是为了图像更接近原文，并非与原文一致；
3）对于双金属单原子单点能计算的SCF部分与Fe-N4及Co-N4计算时的区别主要是减小了charge，步数调整为200，增大了smearing（为了收敛）
4）对于Fe-N4及Co-N4，SCF部分与几何优化部分的参数一致