# Example: Mössbauer with X2C: Hg compounds¶

Download Hg_Mossbauer_X2C.run

This example uses the relativistic spin-orbit coupled X2C method. 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. Typically one needs to perform a fit of the experimentally measured isomer shifts versus the calculated electron densities. 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 qadrupole splittings the key QTENS is required This example calculates the compounds Hg, HgF, HgF2, HgF4, and HgCl2.

$ADFBIN/adf << eor ATOMS Hg 0 0 0 END Basis Type ZORA/DZ Core None End nuclearmodel gaussian exactdensity numericalquality good relativistic spinorbit X2C end input eor rm TAPE21 logfile$ADFBIN/adf << eor
ATOMS
Hg 0 0 0
F  0 0 2.007
END
Basis
Type ZORA/DZ
Core None
End
unrestricted
nuclearmodel gaussian
symmetry nosym
noncollinear
exactdensity
numericalquality good
relativistic spinorbit X2C
qtens
end input
eor
rm TAPE21 logfile

ATOMS
Hg 0 0  0
F  0 0  1.914
F  0 0 -1.914
END
Basis
Type ZORA/DZ
Core None
End
nuclearmodel gaussian
exactdensity
numericalquality good
relativistic spinorbit X2C
qtens
end input
eor
rm TAPE21 logfile


The calculation for HgF4 and HgCl2 are similar as for HgF2. Below the used nuclear coordinates are given.

ATOMS
Hg  0     0     0
F   0    -1.885 0
F   0     1.885 0
F  -1.885 0     0
F   1.885 0     0
END

ATOMS
Hg 0 0  0
Cl 0 0  2.252
Cl 0 0 -2.252
END