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An analysis of predictions by the semi-empirical MNDO molecular orbital method for some aspects of molecular energetics

✍ Scribed by N.Colin Baird; Graham C. Hadley

Publisher
Elsevier Science
Year
1986
Tongue
English
Weight
688 KB
Volume
128
Category
Article
ISSN
0009-2614

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✦ Synopsis

Calculations using the MNDO HE molecular*rbital method predict that NHd, PH4 and H$3 are stable free radicals, and that local minima exist for H30 and H2Cl. The tendency of MNDO to overestimate the stability of such systems is traced to its neglect of overlap integrals. Results for Hz (both ground and excited states) support this conclusion. Stable radicals with formulas BeH3 and BH4 are also predicted. Analysis of hydrocarbon thermochemistry indicates that MNDO fails to predict the correct sign for the relative magnitude of bond interactions, whereas ab initio calculations give the correct sign and approximately the correct magnitude. Finally, it is shown that the apparent superiority of MNDO over ab initio MO calculations in predicting molecular energetics is illusory when the methods are compared on the same basis.

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