Configuration state function

In quantum chemistry, a configuration state function (CSF), is a symmetry-adapted linear combination of Slater determinants. A CSF must not be confused with a configuration. In general, one configuration gives rise to several CSFs; all have the same total quantum numbers for spin and spatial parts but differ in their intermediate couplings.

In quantum chemistry, a configuration state function (CSF), is a symmetry-adapted linear combination of Slater determinants. It is constructed to have the same quantum numbers as the wavefunction, ${\displaystyle \Psi }$, of the system being studied. In the method of configuration interaction the wavefunction can be expressed as a linear combination of CSFs, that is in the form

${\displaystyle \Psi =\sum _{k}c_{k}\psi _{k}}$

where ${\displaystyle \psi _{k}}$ denotes the set of CSFs. The coefficients, ${\displaystyle c_{k}}$, are found by using the expansion of ${\displaystyle \Psi }$ to compute a Hamiltonian matrix. When this is diagonalized, the eigenvectors are chosen as the expansion coefficients. CSFs rather than just Slater determinants can also be used as a basis in multi-configurational self-consistent field computations.

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