Mössbauer spectroscopy

Isomer shifts

By default the electron density at the nuclei is calculated, no input key is required. In the implementation in ADF, the electron density is not calculated exactly at the center of the nucleus, however, at points on a small sphere around the center of a nucleus. The printed electron density in the output of ADF is the average electron density on these points. The radius of the sphere is an approximated finite nuclear radius. The electron density at the nuclei could be used for the interpretation of isomer shifts in Mössbauer spectroscopy. Typically one needs to perform a fit of the experimentally measured isomer shifts and calculated electron densities, like, for example, is done in Ref. [281].

One should use all electron basis sets for the Mössbauer active elements. Important is to use the same basis set, same exchange correlation functional, same integration accuracy, and same nuclear model (see key NUCLEARMODEL), if electron densities at nuclei in different molecules are compared. Note that the absolute electron density at a nucleus heavily depends on the accuracy of the basis set in the core region of this nucleus, especially if relativistic effects are included.

Quadrupole splittings

For the calculation of Mössbauer quadrupole splittings see the key QTENS.

Nuclear resonance vibrational spectroscopy (NRVS)

The nuclear resonance vibrational spectroscopy (NRVS) experiment can be thought of as Mösbauer spectroscopy with vibrational sidebands. The NRVS experiment provides the complete set of bands corresponding to modes that involve motion of the Mössbauer active atoms. In order to calculate this with the ADF program a partial vibrational Density-Of-States (PVDOS) has been implemented. A PVDOS factor for a given atom is the ratio of this atom nucleus kinetic (vibrational) energy to the total vibrational energy of all nuclei, for a given mode. PVDOS factors for every atom and every mode are written to TAPE21 if IR Frequencies are calculated. To visualize the calculated PVDOS use the ADFspectrum program: select the PVDOS spectrum type. Next select one or more atoms to get the PVDOS spectrum generated by the selected atoms. This is useful for analysis of NRVS spectra in bioinorganic chemistry for NRVS-active nuclei.