I would like to calculate the formation energy of P2-Na0.67Fe0.5Mn0.5O2 based on DFT, what should I do step by step. Any help would be appreciated. Thanks.
It depends on the "formation" reaction. Chemists might define formation energy by the material formation from each of its pure elements:
0.67 Na + 0.5 Fe + 0.5 Mn + O2 -> Na0.67Fe0.5Mn0.5O2
(others might define it differently based on how they synthesize the material)
In this case, you can search for the CIF file of each reactant, relax the structure, and obtain the total energy from the SCF calculation. You need to divide the total energy by the number of atoms in your structure to get it in the unit of eV/atom or eV/f.u. Then, calculate the total energy difference (product minus reactant)
Hi Jinpin Wu
Let’s break down the general case so you can apply this method to your specific study.
First, perform the DFT calculations for the pure components and for the compound. The formation energy is given by:
ΔH_f = E_AB - (E_A + E_B)
Where:
E_AB is the total energy of the compound AB.
E_A and E_B are the total energy of the pure element A and B, respectively.
In VASP you do: Set up the POSCAR, INCAR, KPOINTS and POTCAR files for each calculation i.e., for each pure components and for the compound calculation, to obtain E_A, E_B, and E_AB, respectively. You should be familiar with setting up the POSCAR file for each calculation; it’s straightforward (I can assist you further if needed). You can generally use the same INCAR file for both calculations. Ensure your k-grid in the KPOINTS file is sufficiently dense to achieve good results and use the same file for all calculations. I have found that a 5 5 5 grid for bulk and 5 5 1 grid for slabs provides a good balance between accuracy and computacional cost. For the POTCAR file, simply combine the pseudopotentials of interest into a single file (copying and pasting).
Rgds
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