Comparison of Single Point Ab initio Energies Calculated Using 3-21G and AM1 Geometries
Abstract
Single pint ab initio calculations for number of molecules, using various procedures with 3-21G or AM1 geometries, show that the AM1-based results seem to be better for high level ab initio procedures and for studies of reactions, as well as requiring less computing time. Current ab initio methods usually give good estimates of heats of reaction if a large basis set is used and if allowance is made for electron correlation, e.g. by Moeller-Plesset (MP) perturbation theory. However, calculations of this kind require too much computing time to be carried out rigorously, i.e. with full geometry optimization, for any but small molecules. It has therefore become a standard practice in such cases to calculate the geometries by a simple and correspondingly cheap method, usually the 3-21G model, and then to carry out single point calculations by the high level procedure. The same procedure is also commonly used in studies of the Transition States (TS) of reactions where the cost of calculations by a correlated high level procedure is even more forbidding. Reprints.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1989
- Accession Number
- ADA222556
Entities
People
- Andrew J. Holder
- Eamonn F. Healy
- Michael J. Dewar
- Santiago Olivella
Organizations
- University of Texas at Austin