ABSTRACT
Now that we have in hand the algebraic forms necessary to compute useful wave functions for chemical systems, we are able to discuss the implementation of the methods. Here we describe a very simple program capable of illustrating features of the SCF method. It employs small basis sets composed entirely of spherical functions-‘‘s’’ orbitals. Hence its name SCF1s. The choice of basis minimizes the effort to be expended in integral evaluation and permits the structure of the calculation to be seen clearly. The fact that it must apply to only a few atoms and small molecules is precisely what we need in first examples. SCF1s is expressed in FORTRAN(77). The choice of computer language is
partly historical and partly an expression of the universal familiarity of the language. The free WATCOM compiler can process the code into executable files which can run on any PC. There is no graphics interface, but we hardly need anypowerfulmolecule-builder for the small systemswhich arewithin the reach of SCF1s. Details of its use are provided on theCDand in the listing itself.
The SCF1s program can describe single-center systems with exponential Slater-type orbital (STO) 1s functions. Here we describe the He atom with two STOs; the object is to solve the Roothaan equations in the small basis. The program will read from a file called ‘‘scf1s.dat’’
