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I've been conducting a dihedral angle scan on methyl bithiophene in its excited states using Gaussian 16. Despite following standard procedures, my results appear to be incomplete, and I've observed bond breaking in the final step of the structure. I'm seeking insights into potential causes and solutions for these issues.

Details of the Procedure:

  • Software: Gaussian 16
  • Method: Time-dependent DFT (TD-DFT)
  • Functional and Basis Set: B3LYP/6-311g(d)
  • Keywords: #p opt=modredundant td=(nstates=5, root=1) geom=connectivity

Observed Issues:

  • The scan did not complete as expected.
  • Bond breaking occurred in the final step, which is unexpected for the system under study.

Questions:

  1. What are common reasons for incomplete scans in excited state calculations?
  2. How can bond breaking during a dihedral scan be addressed or prevented?
  3. Are there any recommended changes to the input file that could improve the stability and completeness of the scan?

Any suggestions or guidance from those experienced with similar TD-DFT calculations in Gaussian would be greatly appreciated.

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  • $\begingroup$ Breaking of which bond? $\endgroup$
    – Mithoron
    Commented Apr 6 at 15:06
  • $\begingroup$ Breaking one of the bonds in thiophene that is adjacent to the bond connecting two thiophene units. $\endgroup$
    – To'lanboyev Iskandar
    Commented Apr 7 at 17:37

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