ON SOME WAYS OF MODIFYING SEMIEMPIRICAL QUANTUM-CHEMICAL METHODS

The problems of semiempirical quantum chemical calculations of (a) spi n densities in paramagnetic organometallics, (b) hydrogen bonds, and ( c) bond energies and the structure of transition-metal compounds are d iscussed. Some modifications of the existing semiempirical quantum che mical method are presented. An extended NDDO approximation has been de veloped. This scheme includes explicit symmetric orthogonalization of the core Hamiltonian and the use of Hellmann's effective core potentia l for core-electron interaction. (C) 1996 John Wiley & Sons, Inc.