Two-component transformation inclusive contraction scheme in the relativistic molecular orbital theory

The incorporation of a two-component transformation into the contraction coefficients of basis functions is suggested. Such a contraction, referred to as "two-component transformation inclusive contraction (TIC)", effectively eliminates the computational cost associated with the two-component transformation and can be readily implemented into conventional quantum chemistry programs. TIC was verified through numerical calculations using the second- and third-order unitarized Douglas-Kroll method, which is newly derived for the validation of TIC, and the infinite-order two-component method. The numerical validation results suggested that TIC could sufficiently reproduce the results of primitive basis sets for both atoms and molecules.