Hi Guntram,<br><br>In general, the results of an optimization will differ from experiment. This is especially true with vdW-DF, which has been shown to give binding distances that are too large in general. That being said, I agree that the difference between your computed result and experiment seems excessive. Assuming all your atomic coordinates and cell parameters are correct, one potential trouble I see in your input file is the "conv_thr" parameter. 1e-5 is quite a poor convergence criterion, especially for a variable-cell relaxation run. Forces and stresses tend to be harder to converge than energies so you often need very low energy convergence thresholds for relaxation runs. I generally don't run any relaxation calculation without a cutoff of 1e-8 or better. Without seeing your output I can't know if this will help but it's good practice in any case.<br>
<br>If these are ionic systems you're doing, as it seems they are, you might need to do spin-polarization calculations. Unfortunately, there is no rigorous way to do spin polarization at present using vdW-DF. Just as a check you could try a spin polarized run with the Grimme corrections (london=.true. in the &system section). <br>
<br>If you could attach an output file, I might be able to tell you a bit more.<br><br>Hope this helps,<br>Brian<br><br><br><br>