EPW Forum

Dear jack, Thanks for sharing the files. Looking at the results obtained with your inputs, it seems that the spread of the Wannier functions is way too large. In this case, I found that it is more convenient to build a Wannier function set comprising 8 bands (5 valence+3 conduction), so that P:s and ...

Dear jack, Thank you for your post. The error "Non-physical solution, check initial guess and convergence" is issued as a safeguard to prevent unphysical results when there are atomic displacements that exceed half of the lattice parameter. This usually indicates that there’s a problem in your c ...

Dear jack, Yes, the choice of the pseudopotential might affect the electronic structure, phonons, and the electron-phonon matrix elements; as a result it might indirectly influence the polaron formation energy as well. However, the differences should be quantitatively small, and no qualitative ...

Dear jack, From your input file I see that you are using a 6x6x6 k- and a 2x2x4 q-grid. The k- and q- grids need to be commensurate, and these are not, so epw1 should print an error message (as I have reproduced using your file). Please use commensurate k- and q- grids (e.g. 6x6x6k and 2x2x2q, and ...

Dear jack, The current implementation in the polaron module is based on the theory described in this reference: https://doi.org/10.1103/PhysRevB.99.235139 As you can see in Eq. (18), the theory assumes that the atomic configuration in the initial configuration (no extra added/removed electron) is ...

Dear Christoph, Thanks for pointing this out. The polaron formation energy is defined as the energy difference with respect to the periodic insulating crystal with one added/removed electron, so efermi_read should be kept to .false. as it is done by default. The code then sets to zero the KS energy ...

Dear Taifeng Liu, Thank you for your question. Note that in the current implementation the self-interaction is removed for the extra electron (or hole). This means that the polaron eigenvalue, with respect to the conduction (or valence) edge, should be accurate. The value of the band gap itself ...

Hello Pravin Karma, You can get a better-looking figure by just changing the boundaries in VESTA; on the left-hand side, click "Boundary", and change the limits to x(min) =-0.5; x(max)=0.5; y(min)=-0.5; y(max)=0.5; z(min)=-0.5; z(max)=-0.5 Keep in mind is that when solving the polaron equations in a ...

Hi Michael,

At the end of your slurm file I see that the number of requested CPUs is 192. In this example the k/q-grid is 4x4x4 so you can parallelize over 64 pools at most. Could you try reducing the number of CPUs / pools and see if the problem persists?

Best,
Jon Lafuente-Bartolome

Dear Pravin, I agree with Sabya, this error occurs when the number of MPI processes is larger than the number of k-points in the fine grid (where the matrix elements will be interpolated and the polaron equations solved). In the school example (lif.epw2.in), nkf1=nkf2=nk3=4, so the fine grid ...