Electronic structure CNDO method

As presented, the Roothaan SCF process is carried out in a fully ab initio manner in that all one- and two-electron integrals are computed in terms of the specified basis set no experimental data or other input is employed. As described in Appendix F, it is possible to introduce approximations to the coulomb and exchange integrals entering into the Fock matrix elements that permit many of the requisite F, v elements to be evaluated in terms of experimental data or in terms of a small set of fundamental orbital-level coulomb interaction integrals that can be computed in an ab initio manner. This approach forms the basis of so-called semi-empirical methods. Appendix F provides the reader with a brief introduction to such approaches to the electronic structure problem and deals in some detail with the well known Htickel and CNDO- level approximations. 

N. V. Zholtovsky and V. I. Danilov, Quantum Mechanical Study of the Electronic Structure of the Nucleic Acids Bases by CNDO/2 Method. Preprint Inst. Phys. Acad. Sci. Ukr. SSR, Kiev, 1973. 

Theoretical calculations using the semiempirical CNDO/2 method including d- orbital participation in (Id X = O, NH, S Y = S) predicted singlet ground states for these systems as well as substantial n- bond character between the S—C bonds arising from dir-pTr overlap, and very little double bond character in the central C—C bond (74JA1817). There is also considerable contribution to the electronic structure from dipolar canonical forms in (Id X = O, NH Y = S) compared to thieno[3,4-c]thiophene (9) as evidenced by the respective calculated dipole moments of 0.15 and 3.21 D for the former and 0.00 D for the latter. 

The semiclassical model always predicts the most compact cluster equilibrium structure because the binding energy per atom is a direct function of the number of bonds. The EH and CNDO methods, which include electron repulsion effects, predict that the charge, geometry, and energy levels are dependent on the type of site where the cluster is adsorbed. 

The electronic structure of the pyrrolizine anion has been investigated by the HMO-,115 the ASMO-SCF-MI-,117 and a CNDO/2-SCF semiempirical method of Pople-Santry-Segal, taking into account all valence electrons... 

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-... 

In particularly thorough examples of the traditional physical organic approach, Parker (1969) and Abraham (1974) interpreted solvent effects on Walden inversion reactions by using thermodynamic transfer functions. However, in order to explain the reaction rate decrease upon solvation from a microscopic point of view, quantum mechanical electronic structure calculations must be carried out. Micro-solvated Sn-2 reactions were initially studied in this way, with the CNDO/2 semiempirical molecular orbital (MO) method, by using the supermolecule... 

Further evaluations [164,165] have demonstrated the applicability of the fitted system of parameters for calculations of the electronic structure and spectra of numerous complexes of divalent cations using merely the CNDO parametrization for the /-system. In [140,169] the EHCF method is also extended for calculations of the ligands by the INDO, MINDO/3, and SINDO/1 parametrizations. In all calculations the experimental multiplicity (spin) and spatial symmetry of the corresponding ground stales were reproduced correctly. The summit of this approach has been reached in [170] by calculations on the i.s-[Fe(NCS btbipyjo] complex. Its molecular geometry is known both for the HS and LS isomers of the said compound. The calculation... 

Mikheikin et al. (11) have formulated an alternative approach where terminal valencies are saturated by monovalent atoms whose quantum-chemical parameters (the shape of AO, electronegativity, etc.) are specially adjusted for the better reproduction of given characteristics of the electron structure of the solid (the stoichiometry of the charge distribution, the band gap, the valence band structure, some experimental properties of the surface groups, etc.). Such atoms were termed pseudo-atoms and the procedure itself was called the method of a cluster with terminal pseudo-atoms (CTP). The corresponding scheme of quantum-chemical calculations was realized within the frames of CNDO/BW (77), MINDO/3 (13), and CNDO/2 (30) as well as within the scope of the nonempirical approach (16). 

D. F. V. Lewis, C. loannides, and D. V. Parke, Toxicol. Lett., 45, 1 (1989). Prediction of Chemical Carcinogenicity from Molecular and Electronic Structure A Comparison of MINDO/3 and CNDO/2 Molecular Orbital Methods. 

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. 

The first theoretical studies on AI2O3 were of electronic structure and spectra. Photoelectron studies on AI2O3 (Balzarotti and Bianconi, 1976 Gignac et a ., 1985) show a two-peak O 2p valence band with a peak separation of 4-4.7 eV and an overall width of about 8.5 eV (Fig. 4.7). Cluster calculations using the MS-SCF-Aa method (Tossell, 1975a), and the semi-empirical molecular-orbital EHMO (Ciraci and Batra, 1983) and CNDO... 

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... 

Theoretical calculation of a + n electronic structure of nitrobenzenes and nitrotoluenes were carried out by LCAO method and gave a good agreement with electronic spectra and dipole moments [22]. Later the CNDO and ab ittitio calculation for nitro-, dinitro- and trinitrobenzenes gave a very good agreement with spectral features and dipole moments [23]. 

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. 

Early calculations for copper, palladium, and silver clusters were carried out by various investigators using the EH and CNDO methods, and among these is an attempt by Baetzold to take into account the effect of a carbon support on the electronic structure of a palladium cluster.In 1976, Messmer etal. compared the efficacies of the three methods of calcu-... 

The semi-empirical CNDO/2 method has been applied64 to an analysis of the electronic structure and conformation of disulphur decafluoride. The results, in good agreement with the available experimental data, enable the calculation of the electronic terms which determine the shape of the potential surface and a discussion of the electronic non-equivalence of the axial and equatorial fluorine atoms, the chemical bond strength, and the anomalous S—S bond length in the S2F10 molecule. 

H. Pommier, A. Samat, J. Metzger, and R. Guglielmetti, Electronic structure of benzothiazolinic spiropyrans (closed and open forms) by the CNDO/2 method, J. Chim. Phys. 72, 589— 594(1975). 

Chromium- 0) and -(i). An rxtended CNDO/2 method has been used to investigate the energy level distribution and electronic structure of Cr(PF3), as well as other PF3 complexes. The results were compared with experimental data. The metal—phosphorus bonds show large a(P M) and jc(M -> P) charge transfers but small total charge transfers (M - P) which induce on the metal a small positive charge. ... 

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