Title: An efficient relativistic density-matrix renormalization group implementation in a matrix-product formulation,
Abstract: We present an implementation of the relativistic quantum-chemical density
matrix renormalization group (DMRG) approach based on a matrix-product
formalism. Our approach allows us to optimize matrix product state (MPS) wave
functions including a variational description of scalar-relativistic effects
and spin-orbit coupling from which we can calculate, for example, first-order
electric and magnetic properties in a relativistic framework. While
complementing our pilot implementation (S. Knecht et al., J. Chem. Phys., 140,
041101 (2014)) this work exploits all features provided by its underlying
non-relativistic DMRG implementation based on an matrix product state and
operator formalism. We illustrate the capabilities of our relativistic DMRG
approach by studying the ground-state magnetization as well as current density
of a paramagnetic $f^9$ dysprosium complex as a function of the active orbital
space employed in the MPS wave function optimization.