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I want to calculate the electronic band structure for CuWO4 using the GGA+U method. Is it necessary to optimize the structure using the same GGA+U method or only we can incorporate GGA+U parameter in the bandstructure calculation? Actually, I don't have any idea regarding the GGA+U calculation so could you please help me in this regard? Thanking you with regards Jyotirmoy

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I'm not entirely sure why you're asking the question, but I'm going to assume that geometry optimisation with a GGA is straightforward, and it's the Hubbard U which you're concerned about - perhaps because it is harder to converge the SCF, or it takes more computational time.

Generally speaking, you should always optimise your system's geometry with the same exchange-correlation functional that you're using to compute its properties. However, it is often found that varying the Hubbard U term does not affect the forces very much in practice, so you may be able to optimise with the GGA only. If you do, you should definitely check that the forces for the GGA-optimised geometry are still small when you include the Hubbard U term.

See:

Do the U values affect structure optimization with the DFT+U simulation to optimize crystal structure?

for a similar discussion (also linked by Tyberius).

I'm afraid I've never used SIESTA so I can't tell you anything about how to actually do the calculations with it. There is an online tutorial here:

https://docs.siesta-project.org/projects/siesta/tutorials/dft%2Bu/index.html

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