PRDDO parameterization

The PRDDO (partial retention of diatomic differential overlap) method is an attempt to get the optimal ratio of accuracy to CPU time. It has been parameterized for the periodic elements through Br, including the 3rd row transition metals. It was parameterized to reproduce ah initio results. PRDDO has been used primarily for inorganic compounds, organometallics, solid-state calculations, and polymer modeling. This method has seen less use than other methods of similar accuracy mostly due to the fact that it has not been incorporated into the most widely used semiempirical software. 

There are several variations of this method. The PRDDO/M method is parameterized to reproduce electrostatic potentials. The PRDDO/M/FCP method uses frozen core potentials. PRDDO/M/NQ uses an approximation called not quite orthogonal orbitals in order to give efficient calculations on very large molecules. The results of these methods are fairly good overall, although bond lengths involving alkali metals tend to be somewhat in error. 

In general, CNDO/2, INDO, and PRDDO mimic ab initio results by artful and compensating approximations and semiempirical parameters, and they yield reasonable dipole moments and charge distributions. INDO and ZINDO parameterizations are available for relatively many elements in the periodic table, but their predictions can deviate considerably from experiment. 

Divide and Conquer for Semiempirical MO Methods Force Fields A Brief Introduction Force Fields A General Discussion Hyperconjugation MNDO Molecular Mechanics Conjugated Systems Monte Carlo Quantum Methods for Electronic Structure PM3 PRDDO SINDOl Parameterization and Application. 

Currently, semiempirical methods for TM compounds are at the development stage, because the lack of accurate experimental data particularly for energies makes it mandatory that accurate ab initio calculations are used for the derivation of the necessaiy parameters. The recent progress in ab initio and DFT studies of TM compounds has given an impetus for further work in the field of semiempirical methods (see MNDO/d PRDDO Semiempirical Methods Transition Metals and SINDOl Parameterization and Application). A similar situation exists for empirical methods, where accurate parameters for MM calculations can only be derived for a well-defined subclass of TM compounds. This is one reason why the combination of quantum mechanical and MM methods has been proposed as an appropriate method for calculating large TM compounds. ... 

Other semiempirical methods which are available for theoretical studies of TM compounds are PRDDO, ZINDO (Zemer s intermediate neglect of diatomic overlap), SINDOl (symmetrically orthogonalized intermediate neglect of diatomic overlap parametrization one), and EHT (see PRDDO Semiempirical Methods Transition Metals and SINDOl Parameterization and Application). 

Density Functional Theory Applications to Transition Metal Problems Hybrid Methods MNDO/d NMR of Transition Metal Compounds PM3 PRDDO Semiempiriad Methods Transition Metals SINDOl Parameterization and Application Transition Metals Applications. 

---