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I have a planar molecule and a hydrogen atom. I wish to perform single point energy calculation for different configurations of this system where I would place the hydrogen at a certain distance away from the center of mass of the planar molecule.

I have set up the planar molecule such that it is in the XY plane (Z co-ordine zero(approximately)) with its COM at (0,0,0). Basically I want to put the hydrogen atom at different (0,0,z) positions and find the electronic energy. This is the input file I am using:

*# scan ub3lyp/6-311++g(d,p) int=ultrafine scf=xqc*

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1 2
 C                  0.13813800    1.25878700   -0.00021500


H                  0.30168400    2.36487400    0.00005700


C                  1.20739400    0.19371100    0.00012000


H                  2.26666100    0.44051600    0.00017700


C                  0.62471500   -1.03441700   -0.00003100


H                  1.11284800   -2.00793900   -0.00004900


C                 -1.13810000    0.45325300    0.00012300


H                 -2.11780000    0.92562900    0.00023500


C                 -0.83813500   -0.87256400   -0.00005300


H                 -1.52746300   -1.71570300   -0.00008800


H                  0.00000000    0.00000000    3.10000000


X 11 S 20 -0.100000

What more do I need and where do I need it? I am new to these kind of calculations, any help would be greatly appreciated.

andselisk
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Arun
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    Did you run this input file (and as shown in the post)? I recommend you try a trial run on something small and simple and troubleshoot that first. If you still have problems report those in detail. – Buck Thorn Nov 09 '22 at 09:01
  • @BuckThorn I ran this file but it says no variables in Z-matrix error. – Arun Nov 09 '22 at 12:12
  • You need to define the coordinate to step by using z-matrix coordinates; see the manual: https://gaussian.com/scan/ For examples: https://www.cup.uni-muenchen.de/ch/compchem/geom/scan.html – Buck Thorn Nov 09 '22 at 13:04
  • The input file can't work. Get rid of the asterisks. Get rid of the black lines in the structure section. Define a proper z matrix with the (or a) variable to scan through. The last line looks like input to a modredundant keyword, which is a relaxed scan. The scan keyword performs a rigid scan. I'm working from memory here as I can't try and fix it for you, but you probably want to use GIC. Here's some old stuff of mine, try to run these and adjust your setup. https://chemistry.stackexchange.com/q/49483/4945 – Martin - マーチン Nov 10 '22 at 00:49

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