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Relaxed scan along bending mode across linear structure

Bernhard Dick

I want to follow a bending mode from 120 to 240, i.e. the linear structure at 180 is in the middle and presumably a transition state. I try using RSURFACE with DLC, e.g.:

$zmat ifdmod=1 dlc=.t. auto=.t. autofv=.t. ifzmat(1)=2,3,2,4 scan=.t.
DLCTOL=1D-7 ORTTOL=1D-7 CNVTOL=1D-7 NONVDW(1)=1,2 $end

The connectivity of the atoms is 3-2-4-1, and the angle 2-4-1 is always ca. 100. The calculation stops when the angle 3-2-4 gets close to 180 due to convergence problems with the DLCs. I reduced some of the tolerances and played with IFDMOD=0,1,2 and REUSE=T/F, but there are many combinations, and I did not find one that works.

I wonder whether anybody did this before and knows a trick?
best regards, Bernhard

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