Relativistic self-consistent-field methods for molecules. I. Dirac–Fock multiconfiguration self-consistent-field theory for molecules and a single-determinant Dirac–Fock self-consistent-field method for closed-shell linear molecules

A general Dirac–Fock multiconfiguration self-consistent-field (MC SCF) formalism for molecules is presented and the matrix form of the Dirac–Fock MC SCF equations is given for use in the basis set expansion method. As a special case of the general theory, a single-determinant Dirac–Fock SCF theory is derived for closed-shell linear molecules and the expressions are given for the matrix elements, which turn out to be real with a proper choice of phase factor for the basis spinors. The results are presented for H2 and LiH using the Slater-type basis functions and a general discussion of the method and the results is also given.