The density matrix renomination group (DMRG) allows efficient optimization of matrix product state (MPS) wave functions. Since configuration interaction wavefunctions can be conveniently written as MPS, this method allows us to read diverse problems in the field of electron structure and vibrational spectroscopy.

We use the program QCMaquis for this and are also involved in developing this program. The implementation of different Hamiltonian operators as matrix product operators and the coupling to the electron structure program OpenMolcas allow manifold applications.

The MPS wavefunctions provide easy access to so-called orbital entropy masses, which allow us to select active orbital spaces for multireference calculations in an automated way and to study the optimized wavefunctions in a variety of ways, in particular with respect to magnetic couplings. We obtain accurate electronic energies by coupling the MPS wavefunctions with perturbation-theoretic approaches (CASPT2 and NEVPT2), or using density functional theory (short-range DFT).

Publications

• C. J. Stein, M. Reiher, Semiclassical dispersion corrections efficiently improve multi-configurational theory with short-range density-functional dynamic correlation, J. Phys. Chem. A., 124, 2020, 2834.
• C. J. Stein, M. Reiher, autoCAS: a program for fully automated multi-configurational calculations, J. Comput. Chem., 40, 2019, 2216.
• A. Baiardi, C. J. Stein, V. Barone, M. Reiher, Vibrational density matrix renormalization group, J. Chem. Theory Comput., 13, 2017, 3764.
• C. J. Stein, M. Reiher, Automated selection of active orbital spaces, J. Chem. Theory Comput., 12, 2016, 1760.