Complete neglect of differential overlap CNDO calculations

Complete Neglect of Differential Overlap (CNDO) calculations by Naray-Szabo and Surjan (80MI2), however, were interpreted to favor the lactim form 30a of MOT which is in line with the experimental UV spectra. 

Finally, semiempirical complete neglect of differential overlap (CNDO) calculations [145] again emphasize N2 binding to the trigonal cavity, but now with one nitrogen atom at the center of the cavity and the other on the outside of the cluster as shown in Figure 25. 

Fio. 14. Mechanism for oxidation of olefins based on complete neglect of differential overlap (CNDO) calculations. 

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 consistently anomalous (with respect to electrochemical evidence) position of Au has been found by two different groups. According to Kuznetsov etal.,437 the complete neglect of differential overlap (CNDO) method predicts for any given metal a weaker interaction on the more dense surface. Thus the predicted sequence is (111) < (100) < (110) for fee metals such as Cu, Ag, and Au and (0001) < (1100) for hep metals such as Zn and Cd. However, for the most compact surfaces, the calculated sequence is Hg < Ag(l 11) < Cu(l 11) =Zn(0001) < Au(l 11) < Cd(0001). 

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. 

On the basis of complete neglect of differential overlap (CNDO/2) calculations which include silicon p and d orbitals in the basis set, the effect of the trimethylsilyl substituent is due to electron withdrawal by the interaction of both the silicon p and d orbitals with the aromatic ir-system (85). In as much as the silicon p orbitals are primarily involved in the cr and cr orbitals of the trimethylsilyl group, interaction of the silicon p orbitals with the ir-system amounts to a hyperconjugative, v — cr, electron withdrawl (85). 

Polarizability-Kow Relationships Molar polarizabilities can be derived from molecular orbital (MO) calculations by the complete neglect of differential overlap (CNDO) method [42]. The following correlation has been found for polar compounds that contain either hydrogen-bond-accepting or hydrogen-bond-donating groups (alkanols, alkanones, dialkyl ethers, alkanenitriles) ... 

The electronic structures of hydrochlorothiazide 146 and related substances have been determined by the complete neglect of differential overlap (CNDO/2) method (83AF688). The calculation confirms that the diuretic thiazides are electron-accepting, whereas diazoxide 147, a non-... 

As early as in 1972, a theoretical study of the structure of unknown 1,2,3,4-thiatriazole was carried out using the semiempirical complete neglect of differential overlap (CNDO) method <1972JCD73>. Because of the known large discrepancy for the C-S length predicted by semi-empirical calculations compared with the experimental data for l,2,3,4-thiatriazole-5-thiolate <1986ICA71>, this study has only historical interest. 

Baetzold used extended Hiickel and complete neglect of differential overlap (CNDO) procedures for computing electronic properties of Pd clusters (102, 103). It appeared that Pd aggregates up to 10 atoms have electronic properties that are different than those of bulk palladium. d-Holes are present in small-size clusters such as Pd2 (atomic configuration 4dw) because the diffuse s atomic orbitals overlap strongly and form a low-energy symmetric orbital. In consequence, electrons occupy this molecular orbital, leaving a vacant d orbital. For a catalytic chemist the most important aspect of these theoretical studies is that the electron affinity calculated for a 10-atom Pd cluster is 8.1 eV. This value, compared to the experimental work function of bulk Pd (4.5 eV), means that small Pd clusters would be better than bulk metal as electron acceptors. 

The first attempt to give a description of the electronic structure of thiophene including all valence electrons was made by Clark <1968T2663>. He used the complete neglect of differential overlap CNDO/2 method of Pople, Santry, and Segal, modified in order to include 3d-, 4s-, and 4p-AOs for sulfur in the basis set. The results showed a rather large participation of the 3d-orbitals in the sulfur-carbon bond. The calculated population was 0.24 and 0.14 for 3d and 3d,t. respectively. Calculation of the dipole moment made it clear that the effect of the 3d-orbitals was overestimated by the CNDO/2 method. 

Properties such as photoconduc.tivityl l t l and photoluminescence of silicon polymers have been reported because of their wider optical band gap compared with crystalline silicon. Theoretical investigations of silicon polymers have been also reported ll2l-[21] Xakeda, Matsumoto and Fukuchi calculated the electronic structure of polysilane chains using the semi-empirical approach called the Complete Neglect of Differential Overlaps (CNDO) Molecular-Orbital (MO) method They discussed the dependence of the size and... 

X-ray emission rates in simple molecules have been extensively studied by Larkins and his group [10,11]. Larkins and Rowlands [12] made the MO calculations with the complete-neglect-of-differential-overlap (CNDO/2) method and pointed out that there are significant contributions of interatomic transitions to the C K x-ray emission rates in CO, HCN, and CO2 molecules, but relative intensities are less sensitive to inclusion of crossover transitions. Applying the ab initio MO method to CO, they also examined [13] various factors influencing the molecular x-ray emission rate, such as choice of basis set, choice of length and velocity forms, electronic relaxation effect, and interatomic contributions. Phillips and Larkins extended their calculations to other simple molecules [14,15]. 

TTie three methods that have been most widely adopted to calculate DOS curves for clusters are (/) the semi-empirical extended-Huckel (EH) method, (n) the complete-neglect-of-differential-overlap (CNDO) method, and iii) the self-consistent-field Xa scattered-wave (Xa-SW) method. Calculations of electronic structures of many transition- and noble-metal clusters have been reported over the last decade. No attempt is made to summarize them all, because there appears to be a disparity of view among the expert practitioners as to the validities of the various methods of calculation. However, the story to date is as follows. 

Semiempirical quantum chemical calculations using the complete neglect of differential overlap (CNDO/2) method were made for 1,2-dia-minoimidazole (84KGS1396), 1,2-diaminobenzimidazole (85KGS1402), 1-acylamino-1,2,3-triazoles (87JHC1461), and N,N -diazolyls [80JCR(M)-514]. 

True Hiickel molecular orbital calculations, among other limitations, only address TT-electrons. All atom, semiempirical calculations that include both n- and a-electrons were developed originally by Pople and coworkers [17] implementing the method of complete neglect of differential overlap (CNDO), followed by the increasingly rigorous method of intermediate neglect of differential overlap (INDO) [18]. 

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