An Ab Initio HF-LCAO Calculation

Consider then a HF/STO-3G calculation on aspirin (acetylsalicylic acid)  

In chapter 2 I gave you the. pdb file which contains the Cartesian coordinates. We just add a couple of records to define the level of theory (HF/STO-3G), the charge (0) and spin multiplicity (1). 

Extracts from the Gaussian 98 output file follow. 

Gaussian 98 is a complex program with very many options. It is possible to take standard routes through the program (as I have done in this case) or to design your own route. Lines such as 

Of interest is the SCF=Direct option. There are three ways of dealing with two-electron integrals over the basis functions in ab initio HF-LCAO calculations. The Conventional way is to calculate them once and store them on a 

This is part of the Gaussian(R) 98 program. It is based on the Gaussian 94(TM) system (copyright 1995 Gaussian, Inc.), 

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The increase in computer power and the progress in the methodology have allowed the ab-initio calculations of increasingly more complex and larger systems with an increasing number of atoms N (for periodic qrstems N is the number of atoms in the primitive unit cell). In the HF LCAO and DFT PW methods the computer time and memory scales with N like [377,399]. inner only recently that two linear... 

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