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AMPAC Semi-Empirical Problem

  1. Jun 18, 2011 #1


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    I am an undergraduate student being introduced to the world of computational chemistry. I am modeling a reaction using AMPAC semi-empirical methods, and the output file included an error message. I would appreciate some insight.

    The calculation is a chain calculation connecting two structures corresponding to a partial rotation of a molecular rotor. The calculation completed and marked two nodes as potential transition states (node 5 and node 8). Node 5 had two negative vibrations, Node 8 had a single large negative vibration.

    My calculation settings:
    pm6 rhf singlet fullchn lforce t=auto

    Error message:
    Bad Vibration = 8
    Line Number 6495

    Thank you,

  2. jcsd
  3. Jun 18, 2011 #2


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    Science Advisor

    Sorry, but I don't know much about AMPAC. However, I may still be able to help. The error sounds like it is arising from an attempt to read vibrational frequency data from some sort of input or temporary file. This might happen for any number of reasons.

    Does the error arise at the beginning of the calculation when the input is read, or sometime later? Also, what do the calculation settings mean? I understand "pm6", "rhf" and "singlet", but what are the other settings?
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