Approximate ab initio calculations and the method of molecular fragments

Brailsford, David F.

Abstract

A two stage approach to performing ab initio calculations on medium and large sized molecules is described. The first step is to perform SCF calculations on small molecules or molecular fragments using the OPIT Program. This employs a small basis set of spherical and p-type Gaussian functions. The Gaussian functions can be identified very closely with atomic cores, bond pairs, lone pairs, etc. The position and exponent of any of the Gaussian functions can be varied by OPIT to produce a small but fully optimised basis set. The second stage is the molecular fragments method. As an example of this, Gaussian exponents and distances are taken from an OPIT calculation on ethylene and used unchanged in a single SCF calculation on benzene. Approximate ab initio calculations of this type give much useful information and are often preferable to semi-empirical approaches, since the nature of the approximations involved is much better defined.

Citation

Brailsford, D. F. Approximate ab initio calculations and the method of molecular fragments. Presented at Quantum Chemistry - The State of the Art

• Conference Name: Quantum Chemistry - The State of the Art
• End Date: Apr 10, 1974
• Publication Date: Jul 1, 1975
• Deposit Date: Aug 4, 2005
• Publicly Available Date: Oct 9, 2007
• Journal: Quantum Chemistry - The Stae of the Art. Proceedings of SRC Atlas Symposium April 1974
• Peer Reviewed: Peer Reviewed
• Volume: 4
• Series Title: SRC Atlas Symposium
• Keywords: SCF, Molecular orbitals, Gaussian functions, molecular fragments
• Public URL: https://nottingham-repository.worktribe.com/output/1025738
• Additional Information: This is a re-built PDF version of the "final draft" of this conference paper.