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Re: Relaxed scan along bending mode across linear structure

Pedro Silva
pedros@ufp.edu.pt

On Fri Jan 19 '18 3:44pm, Bernhard Dick wrote
---------------------------------------------
>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.:

> \$SURF NDISP1=25 DISP1=5.0 ORIG1=120.0 REUSE=.F. NSURF=1 \$END
> \$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
>
On Fri Jan 19 '18 3:44pm, Bernhard Dick wrote
---------------------------------------------
>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.:

> \$SURF NDISP1=25 DISP1=5.0 ORIG1=120.0 REUSE=.F. NSURF=1 \$END
> \$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
>

I have met some success in these situation by including a nonvdw(1) instruction between one of the ends of the linear structure and an "off"-linear atom. In your case, I would include:
\$zmat nonvdw(1)=3,1

Mon Jan 22 '18 7:34pm
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