In the reaction path search using Gaussian, most people use scan (opt=modredundant) to gradually change the structure, and observe the change of energy and imaginary frequency.
However, one of the most troublesome things about modredundant is that the calculation stops with an error… for example, when three atoms are aligned linearly.
In this article, we’ll show you how to solve that error.
Bend failed for angle Error
If the angle of three atoms becomes 180 degrees during structural optimization, “Bend failed for angle” is displayed as shown below and the calculation stops with an error.
Using GEDIIS/GDIIS optimizer.
Bend failed for angle 37 – 39 – 40
Tors failed for dihedral 38 – 37 – 39 – 40
Tors failed for dihedral 37 – 39 – 40 – 41
Tors failed for dihedral 37 – 39 – 40 – 42
FormBX had a problem.
Error termination via Lnk1e in /opt/gaussian/g09/g09/l103.exe at Wed May 14 04:44:44 2010.
Job cpu time: 0 days 18 hours 52 minutes 4.0 seconds.
File lengths (MBytes): RWF= 1121 Int= 0 D2E= 0 Chk= 33 Scr= 1
Solution１: move the structure a little
First open the error log file using Gauss View. Next, manually move the structure slightly (e.g. 0.1 – 0.3Å).
In the above case, since there is a problem with the arrangement of atoms 37, 39, and 40, the angles and distances of these three atoms should be slightly changed.
Even if you change the structure manually, you may get the same error again. In that case, it is necessary to change the combination of atoms of the modredundant.
Solution 2: Use gaussian03 !
When reading the computational details in the paper, you may notice that some authors use both gaussian 09 and 03.
Some people might think “It’s outdated that they still use g03!”. However, there are some reasons to use gaussian 03.
Gaussian has bugs, available features, and unavailable features for each revision. Some people still use g03 to avoid such problems.
It is said that the error that the calculation stops because three atoms aligned linear does not occur in g03.（reference 1: “老师说过G03好像不会出现这种情况”）
However, there are still some issues. For example, the M06 series and some latest functionals cannot be used with g03 …
If you know better solutions, please let us know!