Dear All,
I have seen many computational papers inwhich people have done adsorption calculations with freezing the catalyst atoms and I also have seen many papers where they haven't.
Correct me if I'm wrong. When substrate gets adsorbed on the catalyst surface then there must be some changes in the catalyst surface and those changes cannot be seen if we freeze the catalyst atoms. I don't understand this.
Why is freezing the catalyst atoms of cluster is necessary using computational approach?
If I do adsorption and reaction pathway calculations without freezing the catalyst atoms then would it be wrong?
Thanks
I suppose it depends on your computer's power:
Optimizing position of metal atoms is VERY computationally expensive. Also, surface atoms are strongly bonded, their position should almost not change at all.
It is because of computational feasibility. Suppose if u have metal surfaces with few layers as catalysts, after its optimization, for interacting with reactants people generally freeze bottom layers except top layer or particular region which is going to interact. It is useful for saving time and computational power.
For periodic DFT calculations, it's a very standard to freeze bottom two layers of four layer slab. Another explanation for this practice is that the slab is held in position by the supports of the catalyst. However, academia is starting to investigate the support/surface interface, and there are many new conclusions (such as electron withdrawing/donating effect of the support, and change in the metal cluster shapes) that may affect the accuracy of this standard practice, and there are still many things we don't know about these interface effects.
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