I want to calculate the formation energy of RbGeX3 perovskite. One of my article i have calculated formation energy using the formula ∆𝐻𝑓𝑜𝑟𝑚 = (𝐸𝑝𝑒𝑟𝑜𝑣𝑠𝑘𝑖𝑡𝑒 − a𝐸Rb − b𝐸𝐺𝑒 − c𝐸𝑋) / (a + b + c). The reviewer asked me that i have calculated formation energy using the gas phase of elements which does not adequately represent the thermodynamic stability of the crystals. Instead, individual components should be in their bulk phases - to make the formation energy a better indicator of the crystal's stability. So, i need to calculate formation energy using bulk phase formula. Can anyone suggest me how to calculate formation energy using bulk phase?
Dear A. Sadat
I calculated formation energy for CsPbI3. CsPbI3 can be divided easily into CsI and PbI2.
CsPbI3->CsI+PbI2
So, in calculation of formation energy of crystal CsPbI3, I used from reference energy of CsI and PbI2 using this formula:
Ef=Et(CsPbI3)-Et(CsI)-Et(PbI2).
I think that this is formula which you are seeking.
In your case, I don't know about RbGeX3 structure. But all perovskite structrues are similar and it should be consist of RbX and GeX2. Then, you have to find stable structure of RbX and GeX2 and calculate their total energies. Then you can find formation energy:
Ef=Et(RbGeX3)-Et(RbX)-Et(GeX2).
I hope that this helps you.
Jasurbek Gulomov
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