<div>Dear CP2K users, I am calculating the energy of a slab (periodic in XY and non-periodic in Z) using CP2K. I have included my original CP2K input file for reference. The problem is that I cannot achieve convergence with UKS. Perhaps it's due to my impatience, but the convergence cannot go below 0.01 after a few hundred iterations. SCAN (including R2SCAN) is known for its difficulty in converging. However, for silicon, it converges well with the same settings, though it doesn't require UKS (this was just for experimentation). After changing the POISSON_SOLVER to IMPLICIT, I observed a slight improvement in the convergence profile. However, it still did not fully converge. Upon adding different options like the ones below, I saw a significant improvement &POISSON PERIODIC XY POISSON_SOLVER IMPLICIT &IMPLICIT BOUNDARY_CONDITIONS NEUMANN NEUMANN_DIRECTIONS Z &END IMPLICIT &END POISSON However, there is a discrepancy between the energy scale where the original script struggled (around -17794 Hartree) and the one shown by this modification (-18097 Hartree). The simulation is still running but seems promising, at least in terms of convergence trend through iterations. My questions are: (1) Are the boundary conditions shown above appropriate for solid metal slab calculations? The energy discrepancy induced by adding options makes me suspicious of using an improper method. Or could it be that we've finally found the correct energy level? (2) Does my original code have an intrinsic problem that prevents convergence, or is it simply a matter of needing more patience to allow it to converge? Thanks in advance, Ji Woong </div> -- You received this message because you are subscribed to the Google Groups "cp2k" group. To unsubscribe from this group and stop receiving emails from it, send an email to <a href="mailto:cp2k+unsubscribe@googlegroups.com">cp2k+unsubscribe@googlegroups.com</a>. To view this discussion on the web visit <a href="https://groups.google.com/d/msgid/cp2k/d664aa41-d272-4e00-96de-70cccaf63af4n%40googlegroups.com?utm_medium=email&utm_source=footer">https://groups.google.com/d/msgid/cp2k/d664aa41-d272-4e00-96de-70cccaf63af4n%40googlegroups.com</a>.