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I am trying to calculate the energy of a hydrogen bond between RCOO- and Tyrosine (figure below). I freeze the O-O bond at 2.8A and calculate the energy by changing the distance between O-H. But when I set O-H distance less than 0.95 it shows error termination.

I used B3LYP/6-31G method. Here, I am giving the error:

Error termination request processed by link 9999.
 Error termination via Lnk1e in /opt/gaussian/g16/prebuilt-avx2/g16/l9999.exe at Thu Nov 16 17:51:36 2023.

This is the input file I created

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  • $\begingroup$ +1 Welcome to our forum! $\endgroup$
    – Camps ♦
    Commented Nov 17, 2023 at 16:55
  • $\begingroup$ You will need to include a bit more of your output. The message listed is shown with almost any Gaussian failure. $\endgroup$
    – Tyberius ♦
    Commented Nov 17, 2023 at 20:30
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    $\begingroup$ +1. Even if you cannot determine the cause of the error by yourself, you can often still determine which part of the output file provides sufficient information for us to help you to determine the error source, and then you can provide at least the minimum amount of information in you post. In this case, it is clear that "Error termination request processed by link 9999" does not uniquely determine the source of the error, since L9999 is responsible for finalizing the calculation, so any error that does not blow the program up straight away may blow it up at L9999. $\endgroup$
    – wzkchem5
    Commented Nov 18, 2023 at 11:50

1 Answer 1

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A short O-H bond (0.86 Å) is often wrongly observed in X-ray crystallography, but should give you no problems other than SCF problems. Having no experience with gaussian, my guess is that you are indeed having SCF problems. Probably it's better to start with a more reasonable structure.

Note, GFN-xTB gives O-H distances of 1.136 Å (donor) and H-O (acceptor) 1.308 Å.

PS. I'm not sure how good b3lyp with a small basis set will work. GFN-xTB might be a better option then, much faster and probably equally reliable structures.

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