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Evaluation of PM3, AM1, and MNDO for calculation of higher energy ionization potentials

✍ Scribed by James E. Gano; E. Jean Jacob; Rebecca Roesner

Publisher
John Wiley and Sons
Year
1991
Tongue
English
Weight
680 KB
Volume
12
Category
Article
ISSN
0192-8651

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✦ Synopsis

Higher ionization energies were calculated with PM3, AMl, and MNDO for three series of molecules, representative small molecules, molecules containing heteroatoms, and sterically congested alkenes. Values from PM3, AM1, and MNDO were compared to experimental values. In most instances, the semiempirical calculations correctly predict the ordering of higher ionization energies. In the absence of steric hindrance, MNDO is the method of choice. Within groups of molecules, AM1 performs better on hydrocarbons, especially twisted hydrocarbons, than PM3. PM3 commonly gives sigma orbitals which are too high in e n e r a compared to related pi orbitals. PM3 performed better than AM1 with molecules containing oxygen, but failed to give the correct geometry for hydrogen peroxide.

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