# Limitations or Known Problems¶

• “T matrix contributions” - i.e. contributions from the perturbed “half-time-differentiated” overlap matrix - are not yet supported. These contributions are only nonzero for perturbations that both a) affect the basis set and b) have frequencies other than zero. The most relevant such kind of perturbation is the magnetic dipole perturbations using London atomic orbitals. Properties consisting of only other kinds of perturbations - such as geometric displacement of the nuclei or electric dipole perturbations - are unaffected by the lack of T matrix contributions.

• Currently we use QcPertInt (defined as QInt type in include/RSPPerturbation.h, and src/fortran/RSPPertBasicTypes.F90 for Fortran APIs) to reprenset several perturbation labels (see OpenRSP Notations and Conventions), in which one label is described by OPENRSP_PERT_LABEL_BIT bits (that can be modified during the step ccmake, see Compile OpenRP).

For the time being, we do not suggest that users change the type of QcPertInt, because other integer types are not supported by OpenRSP yet.

• The current implementation for calculation of residues of response functions is significantly limited in generality. Currently, only electric dipole perturbations and single residues are possible; furthermore, there are significant limitations for the calculation setup. These limitations are described in further detail in the manual of LSDalton in its (at the time of writing unreleased) 2020 version.