Pairwise Distance Directed Gaussians PDDG

A similar approach using Pairwise Distance Directed Gaussian (PDDG) in connection with the MNDO and PM3 methods has also been reported. The idea is related to the concept used in AMI and PM3 by introducing parameterized Gaussian func-... 

The PDDG/PM3 and PDDGAINDO methods are modifications of PM3 and MNDO that add a certain function, called the pairwise distance directed Gaussian (PDDG) function, containing additional parameters, to the core-repulsion function, thereby significantly increasing the accuracy of these methods [M. P. Repasky et al., J. Comput. Chem., 23, 1601 (2002) I. Tubert-Brohman et al., J. Comput. Chem. 25,138 (2004) J. Chem. Theory Comput., 1, 817 (2005)]. 

A second modification recently described by Repasky, Chandrasekhar, and Jorgensen (2002) focuses on improving the core-repulsion functions in MNDO and PM3. In particular, they define a pairwise distance directed Gaussian function (PDDG) to compute a contribution to the nuclear repulsion energy between atoms A and B as... 

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