Complete neglect of differential overlap method

The Complete Neglect of Differential Overlap method (CNDO) ofPople et al. [8,37-39] makes use of the ZDO approximation [Eq. (26)] for all pairs of atomic basis functions. It treats explicitly all valence electrons (e.g., C 2s, C 2p), but neglects completely the... 

The earliest complete neglect of differential overlap method was introduced by Pople and his collaborators in 1965. - This scheme w as parameterized directly on minimum basis set ab initio calculations. ... 

Nitrogen-14 nuclear quadrupole coupling constants in oxazole have been calculated by using the complete neglect of differential overlap method (CNDO/2) including all the valence electrons,232 and from ab initio molecular-orbital wave functions using Gaussian basis sets.234... 

According to quantum-chemical calculations, the metal-H20 interaction has been proposed to be in the sequence Hg < Ag(lOO) < In < Cu(lOO) [81]. Compared to the experimental data, it appears that the positions of In and Ag(lOO) are exchanged. The complete neglect of differential overlap method predicts for any given metal a weaker interaction on the more dense surface [40]. Thus, the predicted sequence is (111) < (100) < (110) for fee metals and (0001) < (1100) for hep metals. However, for the most compact surfaces, the calculated sequence is Hg < Ag(lll) < Cu(lll) Zn(OOOl) < Au(lll) < Cd(0001).Itisdifficult to accept that Zn can be less hydrophilic than Au or Cd, and also that Au can be more reactive than Cu. More recent calculations gave the other order of metals Ag < Au < Cu. This confirms the position of Cu, but Au still appears to be more reactive than Ag [5]. 

Depending on the level of the approximations used for other integrals ZDO methods differ. In the CNDO (complete neglect of differential overlap) method [205,236] all two-electron integrals are approximated by Coulomb integrals according to... 

Other semi-empirical methods used have included the AMI method of Dewar et al. [218], and the CND02/S3 method (a variant of the complete neglect of differential overlap method) applied with some success to P(Ac) and P(Py) [219, 220]. These have in nearly all cases been used in conjunction with initial or following ab initio calculations. 

Ihc complete neglect of differential overlap (CNDO) approach of Pople, Santry and Segal u as the first method to implement the zero-differential overlap approximation in a practical fashion [Pople et al. 1965]. To overcome the problems of rotational invariance, the two-clectron integrals (/c/c AA), where fi and A are on different atoms A and B, were set equal to. 1 parameter which depends only on the nature of the atoms A and B and the ii ilcniuclear distance, and not on the type of orbital. The parameter can be considered 1.0 be the average electrostatic repulsion between an electron on atom A and an electron on atom B. When both atomic orbitals are on the same atom the parameter is written , A tiiid represents the average electron-electron repulsion between two electrons on an aiom A. 

The complete neglect of differential overlap (CNDO) method is the simplest of the neglect of differential overlap (NDO) methods. This method models valence orbitals only using a minimal basis set of Slater type orbitals. The CNDO method has proven useful for some hydrocarbon results but little else. CNDO is still sometimes used to generate the initial guess for ah initio calculations on hydrocarbons. 

A method which is similar to the Pariser-Parr-Pople method for the n electron system and is applicable to common, saturated molecules has been proposed by Pople 28>. This method is called the CNDO complete neglect of differential overlap) SCF calculation. Katagiri and Sandorfy 29> and Imamura et al. °) have used hybridized orbitals as basis of the Pariser-Parr-Pople type semiempirical SCF calculation. 

Various theoretical methods (self-consistent field molecular orbital (SCF-MO) modified neglect of diatomic overlap (MNDO), complete neglect of differential overlap (CNDO/2), intermediate neglect of differential overlap/screened approximation (INDO/S), and STO-3G ab initio) have been used to calculate the electron distribution, structural parameters, dipole moments, ionization potentials, and data relating to ultraviolet (UV), nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), photoelectron (PE), and microwave spectra of 1,3,4-oxadiazole and its derivatives <1984CHEC(6)427, 1996CHEC-II(4)268>. 

A variety of more advanced, all-electron methods of this type Me available, and are generally referred to as semi-empirical calculations. The acronyms used to name the individual methods are descriptive of the manner in which atomic overlap calculations are performed. Among the more widely used semi-empirical methods are those of complete neglect of differential overlap (CNDO/2) (12), modified intermediate neglect of differential overlap (MINDO/3) (13), and modified neglect of diatomic overlap (MNDO) (14). 

A number of papers have appeared recently in which semiempirical quantum mechanical methods, such as the complete neglect of differential overlap (CNDO), incomplete neglect of differential overlap (INDO), or Hiickel methods, have been applied to electron-deficient systems in an attempt to calculate their properties (31, 49, 64, 75, 77, 78, 89, 90, 92). Although the quantitative results of these calculations must be treated with great care, they do provide an indication of some of the parameters that determine formation and stability of electron-deficient bonded systems. 

Returning to the SCE formalism of HE theory, one can proceed in the spirit of an effective Hamiltonian method by developing a recipe for the replacement of matrix elements in the HE secular equation, Eq. (4.53). One of die first efforts along these lines was described by Pople and co-workers in 1965 (Pople, Santry, and Segal 1965 Pople and Segal 1965). The complete neglect of differential overlap (CNDO) mediod adopted the following conventions ... 

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