CNDO molecular orbital

It is interesting to note that while both Harry Kroto and Robert Curl were primarily interested in microwave spectroscopy, they published papers in the field of theoretical chemistry in the 1960s. For example, the paper by R. F. Curl Jr. and C. A. Coulson [Proc. Phys. Soc., 78,831 (1965)], Coulomb Hole in the Ground State of Two-Electron Atoms, resulted from a sabbatical year at Oxford. See also, H. W. Kroto and D. P. Santry, J. Chem. Phys., 47, 792 (1967). CNDO Molecular-Orbital Theory of Molecular Spectra. I. The Virtual-Orbital Approximation to Excited States. 

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... 

A theoretical treatment of 1,2-oxathietane indicates planarity with aS-0 bond length of 1.669 A and a C-S-0 angle of 100.6°. The electronic spectrum was calculated. The character of the HOMO is largely that of the sulfur 3p orbital. A CNDO molecular orbital study of the retrocycloaddition of 1,2-oxathietane 2-oxide to sulfur dioxide and ethylene shows that strong heteroatom asymmetry lifts the stereoelectronic requirement that the thermal fragmentation occur by a suprafacial-antarafacial path. ... 

Table XI. CNDO Molecular Orbital Results for the Highest Occupied Molecular Orbital in the Fluorenyl Carbanion and in the Complex Li(NH3)2Ci3H9 (83)...

Figure 3.7 Model substrates with a zigzag face on graphite for CNDO molecular orbital calculation. (Adapted from ref. 10.)...

CNDO molecular orbital calculations [11] were performed to calculate the 7t charge distribution in substituted anthraquinones. Geometry optimization through energy minimization was prohibited by the size of the anthraquinones, and thus standard molecular bond distances and angles [12] were employed. CNDO calculations were also performed on tautomeric structures of hydroxy-substituted anthraquinones and resonance structures of amino-substituted anthraquinones. 

DAV Davis, D. W., Shirley, D. A. The prediction of core-level binding-energy shifts from CNDO molecular orbitals J. Electron. Spectrosc. Relat. Phenom. 3 (1974) 137. 

Invariant Procedures. Journal of Chemical Physics 43 S129-S135. pie J A and G A Segal 1965. Approximate Self-Consistent Molecular Orbital Theory. II. Calculations with Complete Neglect of Differential Overlap. The Journal of Chemical Physics 43 S136-S149. iple J A and G A Segal 1966. Approximate Self-Consistent Molecular Orbital Theory. III. CNDO Results for AB2 and AB3 systems. Journal of Chemical Physics 44 3289-3296. 

Semiempirical molecular orbital calculations have gone through many stages of refinement and elaboration since Pople s 1965 papers on CNDO. Programs like PM3, which is widely used in contemporary research, are the cumulative achievement of numerous authors including Michael Dewar (1977), Walter Thiel (1998), James Stewart (1990), and their coworkers. 

HyperChem currently supports one first-principle method ab initio theory), one independent-electron method (extended Hiickel theory), and eight semi-empirical SCFmethods (CNDO, INDO, MINDO/3, MNDO, AMI, PM3, ZINDO/1, and ZINDO/S). This section gives sufficient details on each method to serve as an introduction to approximate molecular orbital calculations. For further details, the original papers on each method should be consulted, as well as other research literature. References appear in the following sections. 

The PPP-MO method has proved extremely successful for the prediction of a wide range of colour properties, and it is currently the most extensively used method for this purpose. It does have some deficiencies. For example, the method carries out its calculations based on rc-electrons only and therefore cannot, except in a rather empirical way, account for some of the subtle effects of a-electrons on colour. Among such effects commonly encountered are hydrogen bonding and steric hindrance. As more and more powerful computing facilities become accessible, there is clear evidence that colour chemists are turning their attention towards the use for colour prediction of more sophisticated molecular orbital techniques which take into account all valence electrons, such as the CNDO and ZINDO approaches, and in due course they may well prove to be the methods of choice. However, at the present time, it has not been established with absolute certainty that these methods will routinely provide superior colour prediction properties. 

Molecular Energetics. Molecular energies can be computed in a variety of ways including empirical fixed valence potentials, full force field potentials, and semi-empirical molecular orbital techniques (CNDO-2, INDO, MINDO-3, MNDO, PCILO). 

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>. 

The molecular orbital methods which have been employed for such studies include extended Hiickel theory (EHT), CNDO, and ab initio LCAO-SCF. 

J. A. Pople and G.A. Segal, Approximate self-consistent molecular orbital theory. III. CNDO results for AB2 and AB3 systems, J. Chem. Phys. 44 3289 (1966). 

The theoretical interpretation of the results was made (334) in terms of the molecular orbital perturbation theory, in particular, of the FMO theory (CNDO-2 method), using the model of the concerted formation of both new bonds through the cyclic transition state. In this study, the authors provided an explanation for the regioselectivity of the process and obtained a series of comparative reactivities of dipolarophiles (methyl acrylate > styrene), which is in agreement with the experimental data. However, in spite of similar tendencies, the experimental series of comparative reactivities of nitronates (249) toward methyl acrylate (250a) and styrene (250b) are not consistent with the calculated series (see Chart 3.17). This is attributed to the fact that calculation methods are insufficiently correct and the... 

ANG AO ATA BF CB CF CNDO CPA DBA DOS FL GF HFA LDOS LMTO MO NN TBA VB VCA WSL Anderson-Newns-Grimley atomic orbital average t-matrix approximation Bessel function conduction band continued fraction complete neglect of differential overlap coherent-potential approximation disordered binary alloy density of states Fermi level Green function Flartree-Fock approximation local density of states linear muffin-tin orbital molecular orbital nearest neighbour tight-binding approximation valence band virtual crystal approximation Wannier-Stark ladder... 

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