Computational Lab 2

Calculation of reference atoms and molecules.

Questions:

Record all answers to a word document like Google Docs or Microsoft Word. We will discuss these questions in class.

Pt32 questions

1. What is the final energy of your particle? When reporting these values, remember to use the correct significant figures and units. In this case, the energies are only accurate to the 0.01 and the unit is eV. Your answer should be around -150 eV.
2. Describe how the structure changed as the energy was minimized.
3. What is your calculated cohesive energy? Remember to use significant figures and to include the correct units.
4. How does it compare to the cohesive energy of bulk Pt, -5.84 eV per atom? Is it lower or higher? Remember that a lower cohesive energy means that it is more stable.
5. Would you expect it to be larger or smaller? Think about which one we anticipate to be more stable? A nano-particle or a block of metal? Note that nano-particles are much more reactive than their bulk conterparts.
6. How do your results agree with the expectations? Explain both in term of cohesive energy numbers and in term of stability.

Pt38 questions

7. What is the final energy of your Pt38 particle? This number should be around -187 eV.
8. What is your calculated cohesive energy?
9. Compute the cohesive energy per atom. Divide the cohesive energy of the 32-atom and 38-atom nanoparticles by the number of atoms to find the cohesive energy per particle. What are the per atom cohesive energies for Pt32 and Pt38?
10. Which structure do you find more stable? Use cohesive energies found to justify your answer. Remember that 38 atoms is closer to the bulk than 32 atoms, this should tell you which one you expect to be more stable.
11. Why did we divide by the number of particles when comparing the cohesive energies for the 38-atom and 32-atom nanoparticles?

    38-atom Pd@Pt core shell nanoparticle questions

12. What is your calculated cohesive energy?
13. Compare the cohesive energies of the pure 38-atom Pt nanoparticle and the core/shell 38-atom Pd@Pt nanoparticle. Which particle is more stable?

    38-atom Pt@Pd core shell nanoparticle questions

14. What is your calculated cohesive energy?
15. Has it gone up or down compared to the core/shell? What does this say about its stability relative to 38-atom PdPt?

    Binding energy questions

    Example: E_binding_Pt38+O = E_Pt38+O - E_Pt38 - 1/2*E_O2
16. What is the binding energy of oxygen on Pt38? Your number should be higher than -3 eV (more positive).
17. What is the binding energy of oxygen on Pd@Pt? This number should not be more than a few eV different from that of Pt₃₈.
18. How is it different from the pure Pt particle?

    Your particle questions

19. What particle did you choose?
20. What was the oxygen binding energy? It is very rare for this number to be lower than -6 eV.
    Show your calculation in the form:
    
    E_binding_Particle+O = E_Particle+O - E_Particle - 1/2*E_O2

    Reaction energy changes

21. What is your calculated energy for H₂ and Cl₂? What is your calculated energy change for forming HCl? The energy change should be around -1 eV.
22. What is your calculated energy for H₂ and O₂? What is your calculated energy change for forming water? The energy change should be around -3 eV.
23. What is your calculated energy change for forming carbon dioxide? The energy change should be around -14 eV.
24. Look up the enthalpy of formation for the above three products, what are the experimentally measured values? A good place to start would be the CRC handbook of Chemsitry and Physics database. You can find it listed in the Databases through UT library website.
25. Are those values close to your calculations? Which one is the closest?
26. Why do you think your values is or is not close to experimentally measured ones? What are the differences between your model and the experiments?
27. If you were to improve your modeling, what could you change? (Don't worry about whather or not you could model it right now)

    Literature search

28. Find the paper called Computational screening of core@shell nanoparticles for the hydrogen evolution and oxygen reduction reactions by Corona et. al. published in the Journal of Chemical Physics. The first two authors are former FRI students that completed this lab!
29. Briefly summarize the purpose of this research paper.
30. What are segregation energies? How were they used in this work?
31. In this paper, several promising catalytic material candidates were found for the ORR. Three of these materials were Os@Ag, Ir@Pt, and Ru@Pd. Which of these 3 materials is predicted to have the highest catalytic activity? Which of these 3 materials is predicted to have the lowest catalytic activity?
32. Predict the catalytic ability of "your nanoparticle" using the binding energy you calculated in the Your nanoparticle section. Indicate whether this material binds too strong, too weak, or about right to oxygen.