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jd1828af
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Can anyone explain how pseudopotentials are calculated using density functional theory?
Consult this : Bachelet, G. B. et al. (1982) Phys. Rev. B 26 4199jd1828af said:Can anyone explain how pseudopotentials are calculated using density functional theory?
jd1828 said:does anyone know of where I could find some calculated pseudopotentials for a solid. Ill go for just about any solid, although CO2 is what I would really need. I am just trying to see if my calculations are anywhere close to what they should be.
marlon said:CO2 a solid ?
I do not understand how you can check your calculations without having the pseudo potential file to model the [valence electron] <---> [nucleus + core electrons]-interactions ?
How exactly do you procede ?
I mean, assuming you are doing Hartree Fock or DFT calculations :
1) what software are you using ? Usually, the pseudopotential files (like the ) can be found on the server of the software developer ; like in the case of SIESTA or ABINIT.
2) What basis set are you using (like doubble zeta gaussians) or do you procede with plane waves ?
3) In DFT case, what approximation do you use for the exchange/correlation functional ? LDA, GGA, Hybrid models ? For metals, you must use the LYP-correlation functional of Parr et al (1988) together with the PBE exchange functional of Perdew, Burke and Ernzerhof (1996)
4) Normally, here you would chose your pseudo potential file. If you take one from literature, be sure that it is "transferable". Also, remember that the pseudopotential file that you choose will be partially determined by your exchange/correlation functional. You need to do a lot of benchmarking to get the right one.
The mentioned functionals can all be found in the previous references that i gave you.
marlon
That's a classic problem. Your atomic forces are too big. Normally the threshold (international standard) is below 0.05 eV/angström. To acquire this demand you must perform a atomic position relaxation and a atomic lattice relaxation.jd1828 said:I was getting very strange energies which I found was caused by the cell volume being a little too small.
marlon said:Just to be complete, let me again show you the general way to proceed after you have selected all necessary input data (pseudo potentials, exchange correlation functional, atomic lattice and atomic positions)
1) perform a convergence test with respect to the energy cutoff value
2) perform a convergence test with respect to the selected k-mesh. The bigger the unitcell, the smaller the k-point mesh (due to the inverse connection between Wigner Seitz unit vectors and (reciprocal) Brillouin unit vectors).
Pseudopotentials are effective potentials that are used to simulate the behavior of electrons in a solid or molecule. They are used in calculations because they allow for faster and more accurate calculations by replacing the highly oscillatory behavior of core electrons with a smoother potential.
The pseudopotential for a specific element is determined by fitting it to the all-electron potential. This is usually done by minimizing the differences between the all-electron and pseudopotential wavefunctions and energies through a variational method.
The accuracy of pseudopotential calculations can be affected by several factors, including the choice of pseudopotential, the cutoff energy, the choice of basis set, and the treatment of exchange-correlation effects.
Pseudopotentials are typically used for electronic structure calculations, but they can also be used for other types of calculations such as molecular dynamics simulations. However, their applicability may vary depending on the specific system being studied.
One limitation of using pseudopotentials is that they are not exact representations of the all-electron potential, so there is always some degree of approximation involved. Additionally, pseudopotentials may not accurately capture the behavior of highly localized electrons, and may not be suitable for systems with strong electron-electron interactions.