Besides contributing to a number of quantum chemical software packages, we develop our own codes.


The QCMaquis software suite allows for an efficient optimization of a matrix product state (MPS) wave function based on the density matrix renormalization group algorithm. One of its central feature is the representation of quantum-chemical operators as matrix product operators. The latter provides the necessary flexibility to accommodate abelian and non-abelian symmetries as well as the implementation of non relativistic and relativistic quantum chemical Hamiltonians, respectively, in a unified framework. Our most recent contributions to QCMaquis include the implementation of a genuine relativistic DMRG model. For further information see




The second-order MPS orbital optimization program is our in-house sandbox development platform. The code utilizes the QCMaquis DMRG program to perform any MPS wave function optimization that is required during self-consistent orbital optimization cycles. Its Fortran-based class structure implementation allows for side-by-side implementations of non- and fully-relativistic prototype DMRG-SCF codes as well as for a toy implementation for orbital-optimized ensemble DFT that are currently in progress. For more information stay tuned as this software is not yet publicly available.




OpenMolcas is a freely available quantum chemistry software package. It includes programs to apply many different electronic structure methods — ranging from single-reference to multiconfigurational electron correlation approaches — to chemical systems, but its key feature is the multiconfigurational approach, with methods like CASSCF and CASPT2.
We contribute to the development of OpenMolcas by including our DMRG developments based on the QCMaquis software. To learn more see




DIRAC (Program for Atomic and Molecular Direct Iterative Relativistic All-electron Calculations). The DIRAC program computes molecular properties offering a wide range of single-reference (response) and multi-reference relativistic quantum chemical electron correlation methods. It is named after P.A.M. Dirac, the father of relativistic electronic structure theory. We heavily contribute to the development of the DIRAC package. For further details see




BAGEL is a parallel electronic-structure program licensed under the GNU General Public License. It offers a wide range of multi-reference non- and fully-relativistic quantum chemical electron correlation methods. It is one of the few program packages that allows to treat Gaunt and Breit e-e interactions as well as strong external magnetic fields in correlated calculations. For further details see




The open-source DALTON and LS-DALTON programs are among the most popular and well established programs allowing to perform a wide range of single-reference and multiconfigurational quantum chemical calculations. We contribute to the development of the DALTON package. For further details see


Re(lativistic) Spect(roscopy) program is a freely available computational chemistry program that allows for fast and reliable predictions of spectroscopic properties of closed- and open-shell molecules containing heavy elements. Molecular properties can be modelled within a relativistic full four-component as well as two-component or one-component (non-relativistic) Hamiltonian framework. We contributed to the development of the RESPECT package. To learn more see