Consistent modifications of SINDO1: I. Approximations and parameters

A consistent modification, MSINDO, of the semiempirical MO method SINDO1 is presented. Different basis sets are used for oneand twocenter interactions. The treatment of the core matrix elements in the nonorthogonal basis is retained with changes only for hydrogen and 3d orbitals. Orthogonalization corrections are now restricted to nonvanishing core matrix elements in the INDO approximation. The set of atomic parameters is increased, but bond parameters are no longer used. An automatic nonlinear least-squares algorithm with a restricted step constraint is used for the optimization of parameters. Heats of formation are adjusted with inclusion of zero-point energies obtained by a scaling procedure of the force constant matrix. The present version MSINDO provides significant improvements over previous versions. A brief comparison for ground-state properties of the elements H, C, N, O, F, and Na to Cl is given. Q 1999 John Wiley & Sons, Inc. J Comput Chem 20: 563]571, 1999