Evaluation of the accuracy of PM3, AM1 and MNDO/d as applied to zinc compounds

The applicability of the semiempirical methods PM3, AM1 and MNDO/d for the calculation of zinc complexes and organometallic compounds containing Zn2+ was evaluated. In Part I we compared calculational results with X-ray structural data. The majority of a randomly chosen set of structures could be satisfactorily reproduced by all three methods. MNDO/d appears to be the most adequate method for the description of bio-organic complexes containing Zn2+ but reveals deficiencies in the description of Zn-S interactions. PM3 fails to satisfactorily describe Zn-O interactions in sterically crowded molecules but proves to be the best method for the description of Zn-N complexes. AMI shows a behaviour similar to PM3. However, the errors found for AMI are ca. 30% larger than for PM3. In Part II, optimal geometries and dissociation energies were calculated for model compounds and than compared with high level DFT (B3LYP/6-311 + G(3df,3pd)) and ab initio (CCSD(T)/6-311 + G*) calculations in order to find the source of the errors determined in Part I. PM3 and AM1 underestimate the energy of the Zn-O interaction to a significant extent in accordance with the findings of Part I. Finally, a case study was performed in that essential steps of the carbonic anhydrase catalytic cycle were calculated using a simple model. Despite the acceptable results presented in Part I, MNDO/d failed the case study due to errors based on the original MNDO parametrisation. (C) 2000 Elsevier Science B.V. All rights reserved.