A two-component variant of the Douglas-Kroll relativistic linear combination of Gaussian-type orbitals density-functional method: Spin-orbit effects in atoms and diatomics

The relativistic variant of the linear combination of Gaussian-type orbitals-fitting functions-density-functional (R-LCGTO-FF-DF) was extended from a scalar relativistic approach to a two-component method that includes spin-orbit interactions. The method was applied to the diatomics Au₂, Bi₂, Pb₂, PbO, and TlH using both a local density (LDA) and a gradient-corrected approximation (GGA) of the exchange-correlation functional. Very good agreement for bond length, vibrational frequency, and binding energy was obtained.