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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*

*Title Card Required*

*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.

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    $\begingroup$ 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. $\endgroup$
    – Buck Thorn ♦
    Commented Nov 9, 2022 at 9:01
  • $\begingroup$ @BuckThorn I ran this file but it says no variables in Z-matrix error. $\endgroup$
    – Arun
    Commented Nov 9, 2022 at 12:12
  • $\begingroup$ You need to define the coordinate to step by using z-matrix coordinates; see the manual: gaussian.com/scan For examples: cup.uni-muenchen.de/ch/compchem/geom/scan.html $\endgroup$
    – Buck Thorn ♦
    Commented Nov 9, 2022 at 13:04
  • $\begingroup$ 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. chemistry.stackexchange.com/q/49483/4945 $\endgroup$
    – Martin - マーチン ♦
    Commented Nov 10, 2022 at 0:49

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