Too much Cu groun state energy

[Attique ur Rehman]

hello everyone, I am new to elk. I am calculating Cu ground State energy, and the result I am getting is too large as compared to values available in litrature.
The input file and the TOTENERGY.OUT files are attached. plz guide me if I am wrong somewhere.

[Lars Nordström]

Dear Attique!

Welcome to elk community.
I do not know what your earlier experience is so my answer might not be spot on what you are worrying about ... Then let us know, for instance what energy do you compare with.

You run for a supercell consisting of four atoms per unit cell, what is referred to as the conventional cell for fcc.

With the given setup you have you can simply add two lines in elk.in
primcell
.true.

Then elk will run with corresponding primitive cell, the true fcc cell which would give you the fourth of the total energy you have now. If that makes you happier?

Good luck,
Lars

[Attique ur Rehman]

Thank you Lars for your reply,
I am comparing the energies with a text book, ''Density functional theory, A practical introduction" by David S Sholl. (picture attached). The minimum energy he has calculated for Cu is -3.76ev/atom while when i convert my energy in eV it comes out to br -45,034.5eV/atom. Although he used VASP for his calculaions, but why there is a huge difference?

[Lars Nordström]

Dear Attique!

OK, a little what I assumed.
Calculations in VASP and other popular pseudo-potential methods ignore the core conribution
to total energy. As of Cu 29 electrons you with pseudo potentials only treat at most 11 . Ignoring the deeply bound core states. This definitely affects the total energy ...
Elk on the other hand is an all-elecron approach. Look at eg DOI 10.1126/science.aad3000
for comparisons in accuracy and value.

Again, welcome to elk community and using the all-electron DFT and extended DFT with highest accuracy. However you cannot compare total energies to non-all-electron methods as eg VASP ...

Best wishes,
Lars

[Attique ur Rehman]

Thanks a lot Lars for your kind reply. It was really helpful.

Stay blessed,
Attique