The effects of polarization function on the spin contamination and distribution in β'-Me4P[Pd(dmit)2]2 were studied using the DFT cluster method. Two basis sets, SV and SVP were considered in the calculations, where B3LYP functional was employed in the doublet state of the one-fragment and dimer clusters. The values of <S2> before annihilation for both SV and SVP basis sets are excellent and very close to the perfect theoretical eigenvalue of 0.75. The values of the spin densities at thiolate and thione calculated using SVP were found to be smaller than the ones using SV. The difference, however, is less than eight percent. In contrast, the difference in the spin density at Pd atoms in both monomers is significantly larger for the SVP, being about 21%. The inclusion of polarization function resulted in the shifting of electron density from the sulfur atoms to the central Pd atoms. The calculated spin densities revealed the inhomogeneous distribution of the electron spin in the dimer that leads to the existence of electron-rich and electron-poor regions.
Spin contamination in MP2 and CC2, a surprising issue
