Communication: Four-component density matrix renormalization group

We present the first implementation of the relativistic quantum chemical two-and four-component density matrix renormalization group algorithm that includes a variational description of scalar-relativistic effects and spin-orbit coupling. Numerical results based on the four-component Dirac-Coulomb Hamiltonian are presented for the standard reference molecule for correlated relativistic benchmarks: thallium hydride. (C) 2014 AIP Publishing LLC.