Method PRDDO

These observations are supported by the calculations of Estreicher et al. [9], using the the PRDDO method and density functional theory, the semi-empirical calculations of Percival and Wlodek [10] and ab initio ROHF calculations [11]. They confirm that the most stable state of CeoMu results from the muon bonding itself to one of the carbon atoms from outside the cage. 

Two philosophies have emerged in connection with the various semi-empirical methods (for a review, see Klopman and Evans, 1976). In both cases certain matrix elements are assumed to be negligible, others are computed, and others are chosen according to some criteria. According to one philosophy, the chosen parameters should lead to agreement with exact Hartree-Fock theory. Then, if desired, correlation can be added in some form. Methods called CNDO and INDO are examples of this. A more recent development is the partial retention of diatomic differential overlap (PRDDO) method (see Estreicher et al., 1989). 

Since motion of the host atoms is so essential at the bond-center site, only calculations that allow for relaxation will produce it as a stable site. Among those are recent cluster calculations for Si by Estreicher (1987), who used the PRDDO method as well as ab initio minimal-basis-set... 

Preliminary approximate calculations of the transition state in C2H6 + IIO reaction, also executed by the Partial Reservation of Double-Centered Differential Overlap (PRDDO) method [29, 30] indicate the interaction between masked ethane conformation (with a calculated internal rotation barrier equal 1.3kJ/mol) and the HO radical approaching it in the C—C plane. The distance between C—C and O—O bond sites was taken as the reaction coordinate. It is found that planar structure (II) corresponds to the transition state in the C2H6 + H02 reaction. 

These IP values were calculated by the PRDDO method... 

Fig. 5.8a, b. Region of the attractive potential (inside the reaction funnel ) of the system CH30 +HCONH2 constructed from calculation data [98] by the PRDDO method for three distances 0=C.0 (dj, d2, in A units) a projections of the zero isoenergetic curves onto the equatorial plane b the reaction funnel outside which repulsion of the reactants is observed. (Adapted from Ref. [98], with permission from the American Chemical Society)... 

In this article, the PRDDO method in its latest modified form (PRDDO/M) " is described. Because it is quite different from a methodological perspective than most approximate methods, the methodological aspects of the approach are emphasized here. However, a few typical examples of the usefulness of the method are presented. Finally, the latest derivative of the PRDDO/M approach, called the parametrized electrostatic potential (PESP) will be discussed. PESP is a parametrization of PRDDO/M aimed at reproducing high-quality (MP2/6-31G ) electrostatic potentials, and represents the first attempt to parametrize PRDDO against calculations beyond the ab initio MBS level. 

The PRDDO method employs three mathematically equivalent basis sets. The first (p) consists of pure Slater orbitals. The second (( >) is a Schmidt orthogonalized, principal axes basis (see below). The third basis (X) consists of orthogonal atomic orbitals (OAOs), which are obtained from the 4> basis via a LOwdin symmetric orthogonalization ... 

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