With the help of a recently suggested computational scheme [J. Chem. Phys. 2007, 127, 084101], Mössbauer isomer shifts are calculated within the context of density functional theory, for a series of iron containing compounds. The influence of the choice of a density functional and of the truncation of a basis set on the results of calculations is analyzed. It has been observed that the hybrid density functionals, especially BH&HLYP, provide better correlation with experimental results than pure density functionals. The analysis of basis set truncation reveals that the addition (or removal) of the tightmost primitive functions to a large uncontracted basis set has only a minor influence on the calculated isomer shift values. It is observed that, with the use of a small contracted basis set, a reasonable accuracy for the calculated isomer shifts can be achieved.