WIEN2k-FAQ: How to select RMT radii?

©2001 by P. Blaha, K. Schwarz and J. Luitz

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The determination of Rmt's is at one hand not so crucial, on the other hand it is. Let me try to make a few statements, but it is important that you consider all points, not just one or two.
In addition, it is highly recommended that you use the setrmt_lapw script, which will make a proper selection for you.
  1. In order to save computer time, choose the radii as large as possible. However:
  2. Choosing them smaller will make the calculations more expensive (you will need more plane waves), but usually also more accurate (PWs are better basis functions, reduced linearization error, better series convergence, ...).
  3. If core charge leaks out of the spheres (check :NEC01 in case.scf whether too much charge is missing) you can either:
  4. Do not make your Rmt's too different!!! (even when geometry would allow) Some rules of thumb may be:
  5. When your RMT are larger than 2.5 (2.2 for highest precission) bohr, choose LVNS=6 and consider setting of HDLOs for d and in particular f-states.
  6. For hydrogen in very short C-H, O-H or similar bonds: Select the H sphere radius about half of it's partner (typically C: 1.2, H: 0.6 bohr). Reduce RKMAX (3-4 is sufficient; check!), accept the automatically increased GMAX (case.in2) or use an even bigger one.
  7. Identical atoms (elements) should have identical RMTs.
  8. The standard ionic radii are NOT important in determination of Rmt.

    Peter Blaha,