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<p>Thank you very much for reporting this issue and the fix.</p>
<p><br>
</p>
<p>The funny thing is, that rotdef in SRC_dstart runs without
problem, although the part of the code for finding the symmetry
operations is exactly the same. <br>
</p>
<p>What is different, is that in dstart the rotdef.f routine does
NOT have a symmerization of the positions, while the scf-programs
(lapw0/1,2,so) have an additional symmetrization check of
equivalent positions. This check, however, leads to a small
modification due to some rounding error in the 16th digit in the
positions, and for those atoms, the following code fails, because
the mod(x,one) gives still "one" instead of "zero".<br>
</p>
<p><br>
</p>
<p>Thus there are 2 possible fixes: your patch, and/or removing
this symmetrization. I intend to apply both fixes, because this
symmetrization should not be in the scf programs anyway.</p>
<p><br>
</p>
<p>Thank you very much for the report.<br>
</p>
<div class="moz-cite-prefix">Am 23.01.2021 um 20:02 schrieb Martin
Kroeker:<br>
</div>
<blockquote type="cite"
cite="mid:20210123190238.B1939F00ABA@ruby.chemie.uni-freiburg.de">
<pre class="moz-quote-pre" wrap="">We have recently encountered an unexpected problem with lapw0 returning
"ROTDEF error", claiming "symmetry operation not found" for equivalent
positions of an X,X,X site in spacegroup Fd-3m. (One simplified example
is attached to this message to allow reproducing the problem.)
As it appears, SRC_lapw0/rotdef.f takes turns applying the centering
operations to the calculated distance vector looking for a match - and
then undoes that operation before trying the next, instead of simply
copying back the original value. This demonstrably leads to rounding
errors that can exceed the hardcoded tolerance threshold of 1.5e-7
The attached patch avoids the problem by trivially saving x1 before
the cascade of tests for centered lattices, and restoring it after
each that did not lead to a successful exit from the loop.
</pre>
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