MNDO parameters

Thiel and Voityuk (1992, 1996) described the first NDDO model with d orbitals included, called MNDO/d. For H, He, and the first-row atoms, the original MNDO parameters are kept unchanged. For second-row and heavier elements, d orbitals are included as a part of the basis set. Examination of Eqs. (5.12) to (5.14) indicates what is required parametrically to add d orbitals. In particular, one needs and /ij parameters for the one-electron integrals, additional one-center two-electron integrals analogous to those in Eq. (5.11) (there are... 

Over the next decade MNDO parameters were derived for lithium, beryllium, boron,fluorine, aluminum, " silicon, phosphorus, sulfur, chlorine, zinc, germanium,bromine, iodine, tin, mercury, " and lead. ... 

Here, /ab is given by (16.92), each sum in (16.93) contains two, three, or four Gaussian terms, depending which atom is involved, and the quantities a A> a Qa are parameters. [The expression given for /ab i Dewar et al.,/. Am. Chem. Soc., 107, 3902 (1985) is erroneous.] For example, for H there are three terms in the sum, giving nine additional parameters Uih,. .., Cjn. With this modified core-repulsion function, new optimized values for the original MNDO parameters and optimized values for the parameters in the sums in (16.93) were found. 

Thiel and Voityuk [W.Thiel and A. A. Voityuk,/. Am. Chem. 5oc., 100,616 (1996)] extended MNDO to include d orbitals for many second-row and later elements, giving the MNDOId method. MNDO/d does not add d orbitals for first-row elements, so for a compound containing only C, H, O, and N, MNDO/d is precisely the same as MNDO. Also, it was found that for Na, Mg, Zn, Cd, and Hg, inclusion of d orbitals made little difference, and MNDO/d uses only an sp basis for these elements (but the MNDO parameters for these five elements must be reoptimized in MNDO/d). MNDO/d parameters have been published for Al, Si, P, S, Cl, Br, and I, and the method has also been parametrized for several transition metals. 

Over the next decade MNDO parameters were derived for lithium, beryllium, boron, fluorine, aluminum, silicon, phosphorus, sulfur, chlorine,zinc, germanium, bromine, iodine, tin, mercury, and lead. " In 1983 the first MOPAC program was written, containing both the MINDO/3 and MNDO mediods, which allowed various geometric operations, such as geometry optimization, constrained and unconstrained, with and without symmetry, transition state localization by use of a reaction co-... 

At the present time, AMI parameters for sulfur ate not available, but it is possible to use MNDO parameters for sulfur in AMI calculations. Of immediate interest is how well such a mixed parameter set works. 

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