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 Zn2was evaluated. In Part I we compared calculational results with X-ray struc tural data. The majority of a randomly chosen set of structures could be sa tisfactorily reproduced by all three methods. MNDO/d appears to be the most adequate method for the description of bio-organic complexes containing Zn 2+ but reveals deficiencies in the description of Zn-S interactions. PM3 fa ils to satisfactorily describe Zn-O interactions in sterically crowded mole cules but proves to be the best method for the description of Zn-N complexe s. 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 dissoci ation energies were calculated for model compounds and than compared with h igh 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 signif icant extent in accordance with the findings of Part I. Finally, a case stu dy was performed in that essential steps of the carbonic anhydrase catalyti c cycle were calculated using a simple model. Despite the acceptable result s 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 right s reserved.