Dirac–Fock–Slater calculations for diatomic molecules with a finite element defect correction method (FEM-DKM)

The finite element method (FEM) has been developed into an accurate tool for non-relativistic and relativistic single-particle type descriptions of atoms and diatomic molecules, which has become quite fast. Nevertheless, the efficiency remained unsatisfactory in that most of the FEM points were used up in the core regions even though the molecular orbitals there are atomic-like and simply structured. The joint functional set consisting of atomic orbitals used for an LCAO trial wavefunction and the finite element basis for good convergence, employed as a defect correction method (DKM), remedies this deficiency; the computational effort scales basically linearly with the number of FEM points. Using the DKM we reached the same accuracy about an order faster than with pure FEM.