Inclusion of relativistic effects into ZDO methods. IV. Relativistic CNDO/1

A relativistic, four-component version of the CNDO (complete neglect of differential overlap) method is introduced. This method spans the class of zero-differential-overlap approximation and it utilizes a nonempirical parametrization based on results of atomic Dirac-Fock calculations. The spin-orbit splitting is included implicitly using the relativistic basis set which distinguishes Slater-type functions of the lower and higher component spinors. The method is applicable to closed-shell as well as to open-shell systems. The actual version used is the R -CNDO /1_χ with a variable scaling approach. Applications to molecular geometries, ionization potentials, and energies of spin-orbit splitting are demonstrated for AH, AH₂, AH₃, MH, InX, and HgI₂ molecules at the self-consistent-field level as well as in the second order of the many-body perturbation theory.