| 1:34:39 PM PDT - Wed, Oct 5th 2011 |
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Fatal error in geom_calc_dihedral
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Hi Zhang,
The problem is that in your case the particular dihedral angle is undefined. The reason is that if you have atoms A-B-C-D then the dihedral angle is defined as the angle between the planes defined by A-B-C and B-C-D. These planes are uniquely defined as long as the atoms A-B-C and B-C-D are not on a line. If they are, however, on a single line there is no unique definition of the dihedral angle. If you check the coordinates print below (a coordinates through to d coordinates ) then you'll see that the atoms A-B-C are almost exactly on a line. Hence the error message you are getting.
This explains what the error is but not why you are getting it. Your geometry optimization must somehow be using internal coordinates (maybe forced by constraints on the geometry) that become ill defined along the optimization pathway. This is very likely highly case specific. So you may want to have a look at the geometry and maybe the optimization pathway that got you to this point. This should give you some information as to why you are hitting this problem.
Best wishes,
Huub
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