I have created a graphene supercell using Quantum Espresso and performed a vc-relaxation on it. Now, I need to verify whether the created structure is stable and demonstrate its stability with numerical values. Can I use formation or cohesive energy for this purpose?
I have a multilayer structure formed by C,O,H,N and Cu, for a total of 174 atoms. I am thus using U+J Hubbard methodology as well as Grimme corrections within VASP code.
I am doing some convergence studies on the cut-off energy, however by enhancing the ENCUT I don't seem to observe an asymptotic...
In my phonon calculation utilizing DFPT in VASP for a monolayer material with space group 187, I've noticed that while most of the phonon bands are positive, two of them appear to be straight. What could be the explanation for this observation? [1]: https://i.stack.imgur.com/Q5eCS.png
the frequency of these modes shouldnt depend on k. no matter what wave-vector i pick, harmonic bonds perpendicular to the sheet are stretching or compressing. since the adjacent layers are separated by enough vacuum that they dont interact, the only bonds are the ones in each sheet. for modes polarized along this direction, your system is basically a molecule and the band should be flat
the bands should not be perfectly flat though and the lower band isnt polarized perpendicular to the plane. I suggest converging wrt to supercell size and seeing what you get.
In my phonon calculation utilizing DFPT in VASP for a monolayer material with space group 187, I've noticed that while most of the phonon bands are positive, two of them appear to be straight. What could be the explanation for this observation? [1]: https://i.stack.imgur.com/Q5eCS.png
