Large-scale two-component relativistic quantum-chemical theory: Combination of the infinite-order Douglas-Kroll-Hess method with the local unitary transformation scheme and the divide-and-conquer method

Large-scale two-component (2c) relativistic quantum-chemical (RQC) theory is reviewed. We briefly discuss the theories, advantages, and extensibilities of an overall linear-scaling scheme in 2c relativistic theory. The theory is based on the infinite-order Douglas-Kroll-Hess method, with the local unitary transformation scheme to produce the 2c relativistic Hamiltonian, and the divide-and-conquer method to achieve linear-scaling of Hartree-Fock and electron correlation methods. Furthermore, perspectives for large-scale RQC are explained to bring the practical usage and treatment of light and heavy elements in 2c relativistic calculations close to those in nonrelativistic methods.