Neglect of diatomic differential overlap models

I lie next level of approximation is the neglect of diatomic differential overlap model (NDDO [Pople et al. 1965]) this theory only neglects differential overlap between atomic orbitals on... 

There are known strengths ind weaknesses of each semiempirieal method. The AMI and PM3 models only include s- and p-funetions, which limits their u.sefulncss for most elements of the periodic table that require d-orbitals. Many of the.se elements, however, arc not typically found in most drug-like molecules. More recent advances with MNDO/d include the incorporation of d-functions in the NDDO (neglect of diatomic differential overlap) model."" ""... 

NDDO Approximation. Neglect of Diatomic Differential Overlap approximation. The approximation underlying all present generation Semi-Empirical Models. It says that two Atomic Orbitals on... 

Although ab initio molecular orbital theory and density functional theory can be used to systematically improve the accuracy of X-Pol results for large systems, it is still impractical to use these methods to perform molecular dynamics simulations for an extended period of time. With increased computing power, this will become feasible in the future however, at present, it is desirable to use semiempirical molecular orbital models such as the popular approaches based on neglect of diatomic differential overlap (NDDO) or the more recent self-consistent-charge tight-binding density functional (SCC-method to model condensed-phase and biomacromolecules. 

The neglect of diatomic differential overlap (NDDO) method [236] is an improvement over the INDO approximation, since the ZDO approximation is applied only for orbital pairs centered at different atoms. Thus, all integrals pv Xa) are retained provided p and v are on the same atomic center and A and a are on the same atomic center, but not necessarily the center hosting p and v. In principle, the NDDO approximation should describe long-range electrostatic interactions more accurately than INDO. Most modern semiempirical models (MNDO, AMI, PM3) are NDDO models. 

This latter model is extensively utilized by semiempirical schemes such as the Compete Neglect of Differential Overlap (CNDO), Intermediate Neglect of Differential Overlap (INDO), Neglect of Diatomic Differential Overlap (NDDO), etc. methods (called NDO-family, Pople Beveridge 1970) which represent the quantum chemical tools for studying the electronic structure of larger molecules which are not available for abinitio calculations. We shall not discuss the details of the parametrization of these schemes. The aim of this section is merely to put down the second quantized Hamiltonians of the most frequently used semiempirical methods of this type. ... 

Various NDO schemes differ from CNDO in that they do not utilize fully the ZDO approximation. These schemes are discussed in the book by Pople and Beveridge (1970). In the intermediate neglect of differential overlap (INDO) model the differential overlaps between orbitals on the same atom are kept in one-center two-electron integrals, while the neglect of diatomic differential overlap (NDDO) model neglects only diatomic differential overlaps in any two-electron integral. 

Model calculations were performed on the VAMP [24], DMOL [25, 26], and CASTEP [27] modules of the Materials Studio program package from Accelrys. Full geometry optimizations and vibrational frequency analyses were carried out in all electron approximation using in DMOL the BLYP [28, 29] functional in conjunction with the double-numeric-basis set with polarization functions (DNP) and the IR models were calculated from the Hessians [30], In CASTEP the gradient-corrected (GGA) PBE [31] functional was selected for the density functional theory (DFT) computations with norm conserving and not spin polarized approach [32], In the semi-empirical VAMP method we used the PM3 parameterization [33] from the modified neglect of diatomic differential overlap (NDDO) model to obtain the Hessians for vibrational spectrum models [30],... 

The modified neglect of differential overlap (MNDO) model should probably come next MNDO is like INDO except that MNDO treats the diatomic two-electron integrals more accurately. It retains all two-electron integrals involving monatomic differential overlap, and the paper to read is probably ... 

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