A four-index transformation in Diracʹs four-component relativistic theory

An efficient integral transformation program based on the four-component spinors resulting from the Dirac–Hartree–Fock (DHF) method is implemented in the Rel4d program. By adopting generally contracted spherical harmonic Gaussian-type spinors, the small-component basis functions are almost half as many as the basis expansion with the decoupled scalar spin orbitals. This advantage is exploited to enhance the efficiency in the integral transformation. The present integral transformation program is 4–8 times faster than the pioneering programs of Molfdir and Dirac. As an illustrative example, the CCSD and CCSD(T) methods are successfully applied to the ground state of thallium hydride.