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XVIII.

Bad Calculations

The following links illustrate calculations that produce poor results for certain model chemistries and molecules.

A. Bad geometries

  1. Bad calculated geometries by comparing products of moments of inertia.
  2. Bad calculated bond lengths
  3. List molecules whose point groups differ from experiment
  4. Bad calculated bond lengths sorted by molecule

B. Bad vibrational frequencies

  1. Vibrational frequencies whose frequencies increase from HF/6-31G* to MP2/6-31G*, which may indicate a problematic molecule or a problematic vibrational mode.
  2. Bad predicted vibrational frequencies based on differences and ratios with experimental frequencies

C. Low lying excited state

  1. Excited electronic states by CIS

D. Diagnostics

  1. Molecules with negative natural orbital occupation numbers. A warning that the ground state may be multiconfigurational.