Dear CASTEP users,
I want to determine the chemical stability of the alloy I model using CASTEP by calculating the cohesion energy and the enthalpy of formation from the data calculated. I used the equations (see attached files) that I obtained from this paper, see attached 1-s2.0-S027288421830508X-main.pdf file.
Say I am working on a Cu0.95Ir0.05 alloy with a total number of 4 atoms. And it seem like every time I substitute the final enthalpy values to the equations (see attached equations file) I get positive value, meaning the alloy I am trying to model is unstable. So I am not sure if I am calculating correct or wrong. There is also this total energy value that can be obtained from the optimized geometry structure under energy from the properties explorer, see attached Energy file, what is this energy for? May someone please take me on a step-by-step procedure on how to calculate the cohesion and the enthalpy of formation, you can use any values of your choice for demonstration purpose, and it shouldn’t be correct IrCu, Ir and Cu correct energy values.
Thanks,
Bongani
In the text file (first file shown above), you have to look for " Final energy, E ", which is the energy of optimized system. Then look for "Pseudo atomic calculation performed for Cu" and same for "Ir" to get the total energy of each element species or you can create a large box and insert one element to get its total energy. Then, you can use these result to estimate the cohesive and formation energies.
Thank you for your prompt reply. Please see the attached enthalpy procedure i used to calculate, and I am getting a positive value. Which simple says this alloy composition is not chemical stable. I am of the view I am substituting with wrong information. As for the cohesion, i am lost. Mohammed M. Obeid
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