A graphical scheme for addressing determinants in large configuration interaction treatments

A graphical technique is proposed for generating and addressing all require d alpha and beta strings of spin-orbitals for configuration interaction tre atments based on determinants. Compared with other treatments, this scheme, as well as reducing to a minimum the number of logical operations, avoids entirely the storage of the massive tables and vectors usually required for addressing the determinants. The generation is proposed of all required ad dresses to locate the determinants in the CI vectors, before and after appl ication of the Hamiltonian, at run time using graphs and one intermediate t able of acceptable dimensions. The scheme, which has been tested on a small personal computer, appears ideal when limited computational resources are available for the CI treatment. It is believed also to be useful for larger applications.