We present a comparative density functional theory (DFT) investigation of the interaction of the iron porphyrin (FeP) molecule with the metallic Co(001) and Cu(001) surfaces, with the aim of elucidating the effect of different choices for the treatment of dispersion. We compare a GGA+U approach, several flavors of dispersion-augmented terms, and two variants of the vdW-DF approach, which treats long-range correlation explicitly. For the Co surface, we find that all approaches predict chemisorption and a high-spin state, although vdW-DF functionals generally predict weaker bonds and weaker chemisorption. For the Cu surface, we find that the functionals augmented by pair-wise dispersion once again predict chemisorption and a preferred HS state, but the vdW-DF functionals predict physisorption and a LS state. These results demonstrate the importance of careful assessment of the level of theory at which dispersion is treated, as this may have significant quantitative and even qualitative effects on the predictions made. The results also call for additional experimental data for these systems.
We are working at the Institute of Nano Science and Technology Mohali, one of the leading research institutes in India in the field of Nano Science. INST is located in Chandigarh, one of the major cities of India.