Extension of MNDO to d Orbitals:  Parameters and Results for the Second-Row Elements and for the Zinc Group

The extension of the MNDO formalism to d orbitals is outlined. MNDO/d parameters are reported for Na, Mg, Al, Si, P, S, Cl, Br, I, Zn, Cd, and Hg. According to extensive test calculations covering more than 600 molecules and several properties, MNDO/d provides significant improvements over established semiempirical methods, especially for hypervalent compounds. The mean absolute error in MNDO/d heats of formation amounts to 5.4 kcal/mol for the complete validation set of 575 molecules and is identical for the subsets of 508 normal valent and 67 hypervalent compounds. In addition to the statistical evaluations, several specific applications are briefly discussed to illustrate the performance of MNDO/d in selected areas and to comment on problematic cases.