Calculation of the electronic structures of molecules by the nonempirical NDDO method

Abstract

At present, quantum-chemical calculations are based particularly on methods involving zero differential overlap (ZDO), especially complete neglect of differential overlap (CNDO) [I]. The CNDO method is used, as a rule, in semiempirical form and has been employed with some success in various aspects of quantum chemistry [1-3]. If the parameters are carefully selected, one can obtain good results in calculating certain molecular characteristics such as the energy, bond length, and valence angle, spectroscopic constants [4], etc. However, so far it has not been possible to obtain a set of parameters that enables one to calculate satisfactorily a wide range of molecular characteristics simultaneously. In particular, in [5, 6] the CNDO method did not give satisfactory results for the wave functions and one-electron energy levels. On the other hand, any rigorous structural study of a molecular system, especially a complex, requires calculations on the geometry, energy, and density matrix within the framework of a single system of parameters [7].