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Molecular properties

In the field of molecular properties we develop methods for the calculation
of any user-defined properties within first and second order perturbation theory
for one- and two-component wave functions or electron densities within
Hartree-Fock (HF) or density functional theory (DFT).

Our developments are focused on complex, spin-dependent electron densities
which can also be used within the mean- field approximation that are
assumed in HF and DFT calculations, which can account for spin-polarization correlation
effects. We mostly work with the quasi-relativistic Zeroth Order Regular
Approximation (ZORA), in which the spin-orbit coupling is considered
self-consistently. Within ZORA properties related to the weak interaction [1-4] or
in connection with theories beyond the standard model of particle physics,
such as the electric dipole moment of the electron [5], were derived and
implemented.

Recently, we have developed in our group an approach with which user-defined,
relativistic properties can automatically be transformed and evaluated into the
two-component ZORA framework [6]. Our current research in this area deals with
the calculation of relativistic second order properties in the ZORA image.

[1] R. Berger, N. Langermann and C. van Wüllen, Phys. Rev. A, 2005, 71, 042105.
[2] S. Nahrwold and R. Berger, J. Chem. Phys, 2009, 130, 214101.
[3] T. A. Isaev and R. Berger, Phys. Rev. A, 2012, 86, 062515.
[4] R. Berger and C. van Wüllen, J. Chem. Phys. 2005, 122, 134316.
[5] K. Gaul and R. Berger, J. Chem. Phys., 2017, 147, 014109.
[6] K. Gaul and R. Berger, J. Chem. Phys., 2020, 152, 044101.