Example: Mössbauer spectroscopy: Ferrocene¶
By default in ADF the electron density at the nuclei is calculated, no input key is required. The electron density at the nuclei could be used for the interpretation of isomer shifts in Mössbauer spectroscop. 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. Important is to use the same basis set, same exchange correlation functional, same numerical accuracy, if electron densities at nuclei in different molecules are compared. For the calculation of Mössbauer quadrupole splittings the key QTENS is required For 57 Fe quadrupole splittings will be written in units of mm/s, used in Mössbauer spectroscopy Example shows a calculation on ferrocene with anon-relativistic, and two with a scalar relativistic ZORA Hamiltonian using a different all electron basis set.
First a non-relativistic calculation.
$ADFBIN/adf << eor title ferrocene Atoms FE 0.000000 0.000000 0.000000 C 1.215650 0.000000 1.600813 C 0.375656 -1.156152 1.600813 C -0.983481 -0.714541 1.600813 C -0.983481 0.714541 1.600813 C 0.375656 1.156152 1.600813 C 1.215650 0.000000 -1.600813 C 0.375656 1.156152 -1.600813 C -0.983481 0.714541 -1.600813 C -0.983481 -0.714541 -1.600813 C 0.375656 -1.156152 -1.600813 H 2.310827 0.000000 1.629796 H 0.714085 -2.197727 1.629796 H -1.869498 -1.358270 1.629796 H -1.869498 1.358270 1.629796 H 0.714085 2.197727 1.629796 H 2.310827 0.000000 -1.629796 H 0.714085 2.197727 -1.629796 H -1.869498 1.358270 -1.629796 H -1.869498 -1.358270 -1.629796 H 0.714085 -2.197727 -1.629796 End xc gga blyp end Basis Type TZP Core none End qtens NumericalQuality Good exactdensity End Input eor
Next the scalar relativistic ZORA calculations. ADF will also calculate the quadrupole splittings including the small component density, also called SR ZORA-4. The only difference is the RELATIVISTIC keyword:
relativistic scalar zora
Next a scalar relativistic calculation is performed with a much larger basis set (QZ4P) in the core region. Changing the basis set will have a large effect on the electron density at the nucleus and a noticeable effect on the calculated quadrupole splittings.
Basis Type QZ4P Core none End relativistic scalar zora