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Journal articles on the topic 'Hückel molecular orbital theory'

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Published: 6 September 2023

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1

MORALES-BAYUELO, ALEJANDRO, JUAN TORRES, and RICARDO VIVAS-REYES. "HÜCKEL TREATMENT OF PYRROLE AND PENTALENE AS A FUNCTION OF CYCLOPENTADIENYL USING LOCAL QUANTUM SIMILARITY INDEX (LQSI) AND THE TOPO-GEOMETRICAL SUPERPOSITION APPROACH (TGSA)." Journal of Theoretical and Computational Chemistry 11, no. 01 (February 2012): 223–39. http://dx.doi.org/10.1142/s0219633612500150.

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In this paper some of the characteristic of Hückel method, were exploited in order to obtain some important results, through a new technique with which it is possible to obtain non-degenerate characteristic values as in the case of pyrrole and allowing the expression of conjugated ring systems (Pentalene) as function of a system of diene monomer (Cyclopentadienyl). The local similarity index based on the Hirshfeld partitioning in the framework of conceptual Density Functional Theory (DFT), was introduced in the secular determinant of the Hückel method and was applied to Pyrrole molecule in order to express their orbital energies as a function of the orbital energy of Cyclopentadienyl, to express the energies of molecular orbitals of the Cyclopentadienyl as a function of Pentalene, resolved by the Hückel method and applied to Cyclopentadienyl, by means of six local similarity index: Overlap, Overlap-Interaction, Coulomb, Coulomb-Interaction, with their respective Euclidean distances, using the Topo-Geometrical Superposition Approach (TGSA) as a method of alignment, which allowed us to obtain good results in local similarity indices. This technique will permit the study of some molecular systems that differ in one atom in its molecular structure, resolving the Hückel method for the Pyrrole and Thiophene system without taking into account the considerations with its neighboring atoms. This proposed technique reduces the symmetry of fused ring systems which are Cyclopentadienyl derivatives, allowing to express the orbital energy of a diene dimmer (Pentalene) as a function of diene monomer systems, creating a tool of calculation to solve the problem of obtaining non-degenerate values in systems where the approximations in the Hückel method approximation provide degenerate values and providing a symmetry reduction technique.

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2

Grado-Caffaro, M. A., and M. Grado-Caffaro. "A Molecular-Orbital Model for Amorphous Group IV Semiconductors." Active and Passive Electronic Components 20, no. 1 (1997): 41–44. http://dx.doi.org/10.1155/1997/65485.

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A theoretical model based on standard molecular-orbital theory and extended Hückel approach is proposed. This model is valid for amorphous group IV semiconductors and represents a substantial improvement of the state of the art.

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3

Wolfe, Saul, Zheng Shi, C. E. Brion, James Rolke, Yenyou Zheng, Glyn Cooper, Delano P. Chong, and C. Y. Hu. "Electron momentum spectroscopy of the frontier electrons of DABCO does not support an sp3 hybrid lone-pair description." Canadian Journal of Chemistry 80, no. 3 (March 1, 2002): 222–27. http://dx.doi.org/10.1139/v01-201.

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The highest occupied molecular orbital (HOMO) and next-highest occupied molecular orbital (NHOMO) valence orbital electron density distributions of 1,4-diazabicyclo[2.2.2]octane (DABCO) have been investigated by electron momentum spectroscopy, a technique that probes the orbital-like nature of valence (frontier) electron transfer out of a molecule. The experimental results are compared to a range of 6-311++G** calculations to assess the relative merits of three different orbital models that have commonly been used in chemistry. The delocalized (correlated) canonical KohnSham orbitals calculated using the B3LYP or B3PW91 functionals and density functional theory provide near quantitative agreement with the observed valence electron momentum density distributions, and the delocalized canonical molecular orbitals of HartreeFock (independent particle) theory are in semiquantitative agreement. In contrast, Pauling's widely used and taught valence bond (hybridization) model, which is equivalent to a localized molecular orbital description, does not correspond at all to the experimental measurements. It follows that, for considerations of electron transfer, the "lone pairs" of DABCO are not localized or hybridized, but rather exist as nondegenerate orbitals that are delocalized differently over the molecular framework. The existence of two different experimental valence orbital electron densities of DABCO provides direct confirmation of the frontier orbital HOMONHOMO energy splitting and reordering predicted many years ago by Hoffmann et al. using extended Hückel theory, and interpreted in terms of "through bond" and "through space" interactions.Key words: orbitals, lone pairs, orbital interaction, hybridization.

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4

Sharma, Brahama D. "Molecular Orbital (Hückel) Theory and Linus Pauling: A Historical Perspective." Journal of Chemical Education 73, no. 8 (August 1996): 746. http://dx.doi.org/10.1021/ed073p746.

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5

Langler, Richard Francis, and Laura Precedo. "On the possibilities of π-ylides." Canadian Journal of Chemistry 68, no. 6 (June 1, 1990): 939–41. http://dx.doi.org/10.1139/v90-146.

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A systematic survey of substituted annulenes, using zeroth order Hückel theory, has uncovered a subclass of such structures which are predicted to have very substantial charge separation. An examination of selected structures by MNDO semi-empirical molecular orbital computations provided support for the Hückel descriptions. Such compounds may be of immediate interest to those pursuing synthetic or mechanistic problems which involve cycloaddition reactions. Keywords: π-ylides.

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6

Rashed, Effat A. "Calculations of Constant-Height STM Images of Fullerene C60 Adsorbed onto a Surface." Journal of Spectroscopy 2023 (June 21, 2023): 1–7. http://dx.doi.org/10.1155/2023/8841630.

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Constant-height scanning tunneling microscopy (STM) images of a C60 molecule adsorbed onto a surface were calculated using symmetry-adapted Hückel molecular orbitals (HMOs). Three adsorption orientations of C60 are considered. The interaction between the C60 molecule and the surface was treated using symmetry arguments only. Projection operators were used to generate symmetry-adapted HMOs of the molecule. These orbitals were then used to construct idealized constant-height STM images using the simple tunneling theory of Tersoff and Hamann. A comparison is made with published experimental STM maps. The results show that, for each orientation of C60, split orbitals of the same symmetry have similar appearances in the constant-height maps. They also show that the map of a molecular orbital of a complete degeneracy is dominated by only one or two of its components.

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7

Teschmit, Grit, P. Strauch, A. Barthel, J. Reinhold, and R. Kirmse. "EPR-Einkristall-Untersuchungen an (n-Bu4N)2[Cu(dmit)2] im antiferromagnetisch gekoppelten Wirtsgitter (n-Bu4N)2[(dmit)Cu(tto)Cu(dmit)]: Ein Beitrag zur Aufklärung der sogenannten „paramagnetischen Verunreinigung“ im Wirtsgitter / A Single Crystal EPR Investigation on (n-Bu4N)2[Cu(dmit)2] in the Antiferromagnetically Coupled Host Lattice (n-Bu4N)2[(dmit)Cu(tto)Cu(dmit)]: A Contribution to the Nature of the So-called “Paramagnetic Impurities”." Zeitschrift für Naturforschung B 54, no. 7 (July 1, 1999): 832–38. http://dx.doi.org/10.1515/znb-1999-0702.

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Single-crystal EPR investigations on the paramagnetic CuII impurity present in the binuclear antiferromagnetically coupled complex (n-Bu4N)2[(dmit)CuII(tto)CuII,(dmit)] (dmit = dimercaptoisotrithion, tto = tetrathiooxalate) identify the mononuclear S =½ complex [CuII(dmit)2]2− as being responsible for the observed EPR spectra. The 63Cu hyperfine structure data as well as the data obtained from density functional theory (DFT) and extended Hückel theory molecular orbital (EHT-MO) calculations were used to characterize the spin-density distribution of the copper complex.

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8

Dumont, Randall S. "Effects of charging and polarization on molecular conduction via the source-sink potential method." Canadian Journal of Chemistry 92, no. 2 (February 2014): 100–111. http://dx.doi.org/10.1139/cjc-2013-0227.

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The current−voltage relationships of butadiene and octatetraene are computed using the source-sink potential method with self-consistent Hückel theory. Molecular orbital resonances appear as steps in current, considerably broader than the resonances in the transmission spectrum at any specific bias. This broadening is due primarily to the charging of the molecule as bias increases. A perturbation theory based model is derived to account for the observations. In the case of octatetraene, the HOMO resonance manifests at high voltage when the HOMO energy is raised to the Fermi level of the plus electrode due to the charging of the LUMO and LUMO + 1 levels. Specifically, the LUMO and LUMO + 1 steps in current are augmented by portions of the HOMO contribution to current.

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9

Chauvin, Remi, Christine Lepetit, Valérie Maraval, and Léo Leroyer. "Variation of aromaticity by twisting or expanding the ring content." Pure and Applied Chemistry 82, no. 4 (March 26, 2010): 769–800. http://dx.doi.org/10.1351/pac-con-09-11-07.

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Generalization of the Hückel rule predicts that the (anti)aromaticity of a neutral ring is qualitatively reverted upon a single twist of the π-orbital array (Möbius interconversion), and is preserved upon expansion of all the bonds by single C2 units (ring carbo-merization). These opposite effects are addressed from quantitative theoretical and experimental standpoints, respectively. (i) According to most resonance energy (RE) schemes, the RE value of a Möbius ring is not the opposite of that of the Hückel version. This also applies to the Aihara’s and Trinajstic’s topological resonance energy (TRE), where a non-aromatic reference in the topological limit is defined as being “as identical as possible” to the parent ring but just “acyclic”. In spite of its conceptual merits, the computing complexity and fictitious character of the TRE acyclic reference resulted in a disuse of TRE as a current energetic aromaticity index. Both the calculation and interpretation of TRE have been revisited in light of a cross-reference between the Hückel and Möbius rings within the Hückel molecular orbital (HMO) framework. Whereas the topological influence of triple bonds is currently neglected in the first-level HMO treatment of π-conjugated systems, a graph-theoretical analysis allows one to differentiate the TRE value of a [3n]annulene from those of the corresponding carbo-[n]annulene. The C18 ring of carbo-benzene is thus predicted to be slightly more topologically aromatic than that of [18]annulene. (ii) Recent experimental and density functional theory (DFT) theoretical studies of quadrupolar carbo-benzene derivatives are presented. The results show that the “flexible aromaticity” of the p-C18Ph4 bridge between donor anisyl substituents plays a crucial role in determining the intriguing chemical/spectroscopical/optical properties of these carbo-chromophores.

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10

Litofsky, Joshua, and Rama Viswanathan. "Introduction to Computational Chemistry: Teaching Hückel Molecular Orbital Theory Using an Excel Workbook for Matrix Diagonalization." Journal of Chemical Education 92, no. 2 (November 20, 2014): 291–95. http://dx.doi.org/10.1021/ed500376q.

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11

LETELIER, JORGE RICARDO. "VIBRONIC EXTENDED HÜCKEL THEORY AND THE FORCES IN MOLECULES." International Journal of Modern Physics C 10, no. 07 (October 1999): 1177–92. http://dx.doi.org/10.1142/s0129183199000966.

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A method is presented that allows the computation of the forces acting on the atoms in a molecule along each of the symmetry nuclear displacements coordinates. The method works within the Extended Hückel formalism and makes use of the standard output of a charge-iterated calculation. In this work, examples are given of the different contributions to the total force, arising from the populated molecular orbitals, that act on the atoms in several diatomic molecules and the shape of the vibrational potential is analyzed. Also, the distortions (Peierls) that take place in a linear triatomic system of hydrogen atoms is also examined under this viewpoint.

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12

Mantela, Marilena, Constantinos Simserides, and Rosa Di Felice. "LCAO Electronic Structure of Nucleic Acid Bases and Other Heterocycles and Transfer Integrals in B-DNA, Including Structural Variability." Materials 14, no. 17 (August 30, 2021): 4930. http://dx.doi.org/10.3390/ma14174930.

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To describe the molecular electronic structure of nucleic acid bases and other heterocycles, we employ the Linear Combination of Atomic Orbitals (LCAO) method, considering the molecular wave function as a linear combination of all valence orbitals, i.e., 2s, 2px, 2py, 2pz orbitals for C, N, and O atoms and 1s orbital for H atoms. Regarding the diagonal matrix elements (also known as on-site energies), we introduce a novel parameterization. For the non-diagonal matrix elements referring to neighboring atoms, we employ the Slater–Koster two-center interaction transfer integrals. We use Harrison-type expressions with factors slightly modified relative to the original. We compare our LCAO predictions for the ionization and excitation energies of heterocycles with those obtained from Ionization Potential Equation of Motion Coupled Cluster with Singles and Doubles (IP-EOMCCSD)/aug-cc-pVDZ level of theory and Completely Normalized Equation of Motion Coupled Cluster with Singles, Doubles, and non-iterative Triples (CR-EOMCCSD(T))/aug-cc-pVDZ level of theory, respectively, (vertical values), as well as with available experimental data. Similarly, we calculate the transfer integrals between subsequent base pairs, to be used for a Tight-Binding (TB) wire model description of charge transfer and transport along ideal or deformed B-DNA. Taking into account all valence orbitals, we are in the position to treat deflection from the planar geometry, e.g., DNA structural variability, a task impossible for the plane Hückel approach (i.e., using only 2pz orbitals). We show the effects of structural deformations utilizing a 20mer evolved by Molecular Dynamics.

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13

WANG, Dan. "Application of Simplified Hückel Molecular Orbital Theory to Judge the Geometric Configuration of H₄ and Its Molecular Ions." University Chemistry 33, no. 3 (2018): 84–86. http://dx.doi.org/10.3866/pku.dxhx201711020.

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14

Aragoni, M. Carla, Massimiliano Arca, Francesco A. Devillanova, John R. Ferraro, Francesco Isaia, Francesco Lelj, Vito Lippolis, and Gaetano Verani. "An experimental and theoretical approach to phosphonodithioato complexes: molecular orbital analysis by hybrid-DFT and EHT calculations on trans-bis[O-alkyl-phenylphosphonodithioato]NiII, and vibrational assignments." Canadian Journal of Chemistry 79, no. 10 (October 1, 2001): 1483–91. http://dx.doi.org/10.1139/v01-163.

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The synthesis and the full spectroscopic characterization (FT-IR, FT-Raman, 31P CP MAS NMR) of trans-bis[O-ethyl-phenylphosphonodithioato]NiII (3) are reported. On the basis of hybrid-Density Functional Theory (DFT) calculations and Extended Hückel Theory (EHT) calculations, performed on the simpler trans-bis[O-methyl-phenyl phos phono dithioato]NiII (2) model complex, the electronic structures of phosphonodithioato complexes in their ground states are fully described, and in particular the vibrational features are deeply analyzed, allowing an unprecedented insight into the vibrational features of trans-bis-O-methyl-phenylphosphono- and trans-bis(isopropylamidophosphono)-dithioato complexes of nickel(II), palladium(II), and platinum(II).Key words: phosphonodithioato complexes, IR, Raman, DFT calculation.

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15

TO, TRAN THINH, and STEFAN ADAMS. "CHARGE TRANSPORT AND LIGHT ABSORPTION IN CONJUGATED SYSTEMS FROM EXTENDED HÜCKEL METHOD AND MARCUS THEORY." International Journal of Computational Materials Science and Engineering 01, no. 02 (June 2012): 1250020. http://dx.doi.org/10.1142/s2047684112500200.

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A simple first principle model was developed based on extended Hückel-type orbital calculation, Marcus electron transport theory and two-dimensional-electron-gas model for the treatment of charge transport in conjugated polymers. Though simple and easy to compute, the effect of the applied electric-field is factored in. Based on this, a complete one-dimensional device model with a single layer of conjugated polymer sandwiched between two electrodes was developed with poly(3-hexylthiophene) (P3HT) as a case study. Simulated J-V curves show that π-π charge transport is much more pronounced than intra-chain transport, hence agree with previous findings. Using the same framework, we also calculated the absorption spectra of P3HT by considering the electronic energy barrier for electronic transitions that would satisfy Franck–Condon principle. Absorption spectra closely harmonize to experimental UV-Vis result. The model also reveals intra-chain electronic transitions to be the dominant absorption mechanism. All parameters of the model are obtained from either ab-initio Density Functional Theory (DFT) or Molecular Dynamics (MD) calculations, so that this model is capable of predicting charge transport and light absorption properties of new conjugated polymers without introducing fit parameters.

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16

COLLADO, J. R. ALVAREZ. "ON THE DIAGONALIZATION OF HERMITIAN MATRICES, AND ITS USE TO CALCULATE THE HÜCKEL ELECTRONIC STRUCTURE OF LARGE CARBON NANOTUBES." Journal of Theoretical and Computational Chemistry 06, no. 03 (September 2007): 477–85. http://dx.doi.org/10.1142/s0219633607003106.

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In this paper, a method for calculating all the Hückel molecular orbitals (MO) of large (16.000 atoms) carbon zigzag nanotubes is presented. These MO have been obtained by combining the singular value decomposition (SVD), the Sylvester–Hadamard transform, and the theory of Hamiltonian–Symplectic matrices. Numerical diagonalization of hermitian matrices is reviewed and improved. A new, more advantageous, (tri-diagonal) algorithm is proposed and analyzed. The reactivity of the atoms is described by calculating their free valence indices.

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17

Sherman, Douglas Franklyn, Daniel Dilella, and Kenneth J. Miller. "Partitioning of molecular systems and subsystem replacement by single-centered perturbations: II. Applications of the pseudo substituent technique within hückel molecular orbital theory." International Journal of Quantum Chemistry 8, S8 (June 18, 2009): 187–99. http://dx.doi.org/10.1002/qua.560080823.

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18

Nagaoka, Shin-ichi, Tatsunobu Kokubo, Hiroyuki Teramae, and Umpei Nagashima. "Practical Training in Simple Hückel Theory: Matrix Diagonalization for Highly Symmetric Molecules and Visualization of Molecular Orbitals." Journal of Chemical Education 95, no. 9 (August 8, 2018): 1579–86. http://dx.doi.org/10.1021/acs.jchemed.8b00244.

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19

Nagaoka, Shin-ichi, Yoshinori Yamasaki, Hiroyuki Teramae, Umpei Nagashima, and Tatsunobu Kokubo. "Addition to “Practical Training in Simple Hückel Theory: Matrix Diagonalization via Tridiagonalization, Cyclobutadiene, and Visualization of Molecular Orbitals”." Journal of Chemical Education 97, no. 8 (July 20, 2020): 2373–74. http://dx.doi.org/10.1021/acs.jchemed.0c00857.

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20

Ramakrishnan, Raghunathan. "A Simple Hückel Molecular Orbital Plotter." Journal of Chemical Education 90, no. 1 (November 19, 2012): 132–33. http://dx.doi.org/10.1021/ed300085g.

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21

Liu, Yue, Ying Liu, and Michael G. B. Drew. "Correlation between Fourier series expansion and Hückel orbital theory." Journal of Mathematical Chemistry 51, no. 2 (October 12, 2012): 503–31. http://dx.doi.org/10.1007/s10910-012-0092-9.

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22

Gutman, Ivan. "Hückel Molecular Orbital Energies and Bond Orders of Cyclacenes." Polycyclic Aromatic Compounds 8, no. 4 (January 1996): 251–57. http://dx.doi.org/10.1080/10406639608048352.

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23

Rousseau, R., R. Aroca, and M. L. Rodríguez-Méndez. "Extended Hückel molecular orbital model for lanthanide bisphthalocyanine complexes." Journal of Molecular Structure 356, no. 1 (October 1995): 49–62. http://dx.doi.org/10.1016/0022-2860(95)08905-b.

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24

Hudson, R. F. "The Extended-Hückel perturbation theory and the concept of orbital balance." Journal of Molecular Structure: THEOCHEM 261 (July 1992): 91–112. http://dx.doi.org/10.1016/0166-1280(92)87068-b.

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25

Slee, Tom S., and Preston J. MacDougall. "The correspondence between Hückel theory and ab initio atomic charges in allyl ions." Canadian Journal of Chemistry 66, no. 11 (November 1, 1988): 2961–62. http://dx.doi.org/10.1139/v88-459.

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Atomic charges for the allyl cation and anion are reported, as defined by the quantum theory of atoms in molecules. An interesting feature of these charges is that they differ considerably from expectations based on simple π orbital models. The reasons for the difference are investigated and it is shown that the charges are both compatible with and understandable in terms of simple orbital models.

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26

Gutman, I., Y. Hou, H. B. Walikar, H. S. Ramane, and P. R. Hampiholi. "No Hückel graph is hyperenergetic." Journal of the Serbian Chemical Society 65, no. 11 (2000): 799–801. http://dx.doi.org/10.2298/jsc0011799g.

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If G is a molecular graph with n vertices and if ?1, ?2, ..., ?n are its eigenvalues, then the energy of G is equal to E(G) = |?1| + |?2|+ ... + |?n|. If E(G) > 2n - 2, then G is said to be hyperenergetic. We show that no H?ckel graph (= the graph representation of a conjugated hydrocarbon within the H?ckel molecular orbital model) is hyperenergetic.

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27

Zahedi, Mansour, and Mohammed Al-Kobaisi (Latif). "Resonance Stabilization Study of Some Fullerenes Cn(20 ≤ n ≤ 88): Is n = 32 a ‘Magic’ Number?" Journal of Chemical Research 23, no. 1 (January 1999): 52–53. http://dx.doi.org/10.1177/174751989902300132.

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A π-orbital axis vector (POAV) analysis used in Hückel molecular orbital approximation calculations indicates that the cutoff in the fullerene mass spectrum at C n ( n = 32) must naturally occur with no need to define a ‘magic’ number.

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28

Dias, Jerry Ray. "Valence-Bond and Hückel Molecular Orbital Diradicals—Alternant versus Nonalternant Effects." Australian Journal of Chemistry 56, no. 12 (2003): 1225. http://dx.doi.org/10.1071/ch02221.

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Two distinct classes of diradicals are examined and compared. Valence-bond diradicals are topologically enforced, whereas Hückel molecular orbital diradicals can undergo skeletal distortions and transform to a nonradical form and tend to gain or lose electrons to form stable polyions. Alternant hydrocarbon diradicals are nonpolar species and nonalternant hydrocarbon diradicals tend to be polar species and less prevalent.

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29

Matito, Eduard, Ferran Feixas, and Miquel Solà. "Electron delocalization and aromaticity measures within the Hückel molecular orbital method." Journal of Molecular Structure: THEOCHEM 811, no. 1-3 (June 2007): 3–11. http://dx.doi.org/10.1016/j.theochem.2007.01.015.

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30

Dias, Jerry Ray. "Facile construction of polyene molecules with high hückel molecular orbital degeneracy." Tetrahedron Letters 32, no. 36 (January 1991): 4659–60. http://dx.doi.org/10.1016/s0040-4039(00)92274-3.

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31

Wissner, Allan. "HMO Version 1.1: A Hückel molecular orbital program for the Macintosh." Tetrahedron Computer Methodology 3, no. 2 (1990): 63–71. http://dx.doi.org/10.1016/0898-5529(90)90109-l.

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32

Trinajstić, Nenad. "New developments in Hückel theory." International Journal of Quantum Chemistry 12, S11 (June 18, 2009): 469–77. http://dx.doi.org/10.1002/qua.560120854.

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33

Dowd, Paul. "Unusual hückel molecular orbital degeneracy or some non-alternant, no-kekulé molecules." Tetrahedron Letters 32, no. 4 (January 1991): 445–46. http://dx.doi.org/10.1016/s0040-4039(00)79463-9.

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34

Radhakrishnan, T. P. "Ground state spin of some molecules with unusual hückel molecular orbital degeneracy." Tetrahedron Letters 32, no. 35 (January 1991): 4601–2. http://dx.doi.org/10.1016/0040-4039(91)80050-g.

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35

Zhao, Ming, and Benjamin M. Gimarc. "Three-dimensional Hückel molecular orbital energy level correlation diagrams for polyhedral rearrangements." Polyhedron 14, no. 10 (May 1995): 1315–25. http://dx.doi.org/10.1016/0277-5387(94)00407-6.

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36

Dias, Jerry Ray. "Facile calculation of Hückel molecular orbital eigenvalues of short (n,0) nanotubes." Chemical Physics Letters 647 (March 2016): 79–84. http://dx.doi.org/10.1016/j.cplett.2016.01.055.

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37

Krivul’ko, K. F., and A. P. Klishchenko. "Taking into account universal intermolecular interactions by the Hückel molecular orbital method." Journal of Applied Spectroscopy 73, no. 5 (September 2006): 748–52. http://dx.doi.org/10.1007/s10812-006-0149-2.

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38

Peric, Miljenko, Ivan Gutman, and Jelena Radic-Peric. "The Hückel total π-electron energy puzzle." Journal of the Serbian Chemical Society 71, no. 7 (2006): 771–83. http://dx.doi.org/10.2298/jsc0607771p.

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In spite of being based on drastic simplifications, the H?ckel molecular orbital (HMO) quantum-mechanical model provides a reasonably good description of the properties of ?-electrons in conjugated molecules. The HMO approach is found to be particularly successful in the case of the total ?-electron energy (E), by means of which it is possible to calculate enthalpies of formation and similar thermodynamic characteristics of conjugated compounds. In this paper it is shown that expressions equivalent to E can be deduced within much more accurate quantum mechanical considerations. This might explain why E agrees so well with experimental findings.

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39

Gill, Wendy R., Marion E. Jones, Kenneth Wade, William W. Porterfield, and Edward H. Wong. "Stability patterns in borane cluster chemistry rationalised by extended Hückel molecular orbital studies." Journal of Molecular Structure: THEOCHEM 261 (July 1992): 161–74. http://dx.doi.org/10.1016/0166-1280(92)87074-a.

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40

KENNEDY, R. V., and J. E. ALLEN. "The floating potential of spherical probes and dust grains. II: Orbital motion theory." Journal of Plasma Physics 69, no. 6 (November 25, 2003): 485–506. http://dx.doi.org/10.1017/s0022377803002265.

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Probe theory is generally used to find the potential of dust particles immersed in plasma. The orbital motion limited theory (OML) is often used to find the potential at the probe surface, but the assumptions underlying this theory are usually not valid in the case of dust and the more general orbital motion (OM) theory is much harder to calculate. Solutions are given for the OM theory in a range of cases applicable to dust. It is shown that the surface potential the full theory gives reduces to the OML result for small probes. Commonly in dusty plasmas the OML surface potential is used, with the surrounding distribution given by Debye–Hückel, or Yukawa theory. This form, however, neglects ion depletion due to the absorption of particles on the probe surface. In this paper a new analytical solution to the system is given which is applicable to small probes and dust. This new expression is equivalent to Yukawa form, but takes ion absorption into account.

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41

Baum, James Clayton, Eric Donald Martin, Jack Leon Ginsburg, and Richard Francis Langler. "Anticipating molecular polarity 1: a back-of-the-envelope approach to topologically induced polarity in non-alternant monocycles." Canadian Journal of Chemistry 73, no. 10 (October 1, 1995): 1719–26. http://dx.doi.org/10.1139/v95-210.

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Perturbation theory is applied to fully π-bonded non-alternant monocycles at the Hückel level. An effective "back-of-the-envelope" approach is developed that permits one to anticipate Hückel charge patterns for these monocycles. Very little modification is required to alter the basic approach so that it will permit rapid anticipation of AM1 -calculated charge patterns for such compounds. Keywords: hydrocarbon polarity, perturbation theory.

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42

Wang, Xiang-Yang. "Orbital binding effect in molecular orbital theory." International Journal of Quantum Chemistry 50, no. 3 (April 15, 1994): 197–205. http://dx.doi.org/10.1002/qua.560500305.

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43

Zeyrek, C. Tugrul. "Importance of Orbital Complementarity in Spin Coupling through Two Different Bridging Groups in Dicopper(II) Complexes of Endogenous Alkoxo Bridging Ligand with Exogenous Carboxylate: Ab-initio and Semi-Empirical Calculations." Zeitschrift für Naturforschung A 62, no. 7-8 (August 1, 2007): 409–16. http://dx.doi.org/10.1515/zna-2007-7-810.

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The influence of overlap interactions between the bridging ligands and the metal d orbitals on the super-exchange coupling constant are studied by means of ab-initio restricted Hartree-Fock molecular orbital calculations. The interaction between the magnetic d orbitals and the HOMOs of the carboxylate oxygen atoms are investigated in homologous asymmetrically dibridged dicopper(II) complexes which have significantly different - 2J values (the energy separation between the spin-triplet and spin-singlet states). In order to determine the nature of the fronter orbitals, extended Hückel molecular orbital (EHMO) calculations are also reported. The differences in the magnitude of the coupling constants and magnetic behaviour are rationalized in terms of the bridging ligand orbital complementary / countercomplementary concept.

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44

Galvão, Adelino M., and João L. Ferreira da Silva. "Analysis of 1H NMR Data for Arene-Metal Complexes Using Extended Huckel Calculations." Collection of Czechoslovak Chemical Communications 63, no. 3 (1998): 299–304. http://dx.doi.org/10.1135/cccc19980299.

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This work reports the use of extended Hückel molecular orbital (EHMO) calculations to correlate pz electronic densities of aromatic carbons in group VI metal-bis(η6-arene) complexes with the respective 1H NMR chemical shifts. The effect of delocalization on the acceptor properties and stabilization of ligand orbitals is analyzed comparing complexes of naphthalene, biphenyle and fluorene.

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45

Rodríguez, Leonardo J., and Fernando Ruette. "Semiempirical molecular orbital theory." Journal of Molecular Structure: THEOCHEM 287 (November 1993): 179–84. http://dx.doi.org/10.1016/0166-1280(93)87220-8.

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46

Masamura, Masao. "A simple algorithm for determining total electronic energy by the extended Hückel molecular orbital method." Computers & Chemistry 11, no. 4 (January 1987): 299–300. http://dx.doi.org/10.1016/0097-8485(87)85007-6.

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47

Johnston, R. L., P. J. Knowles, and J. N. Murrell. "Chapter 6. Molecular orbital theory." Annual Reports Section "C" (Physical Chemistry) 87 (1990): 173. http://dx.doi.org/10.1039/pc9908700173.

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48

Couty, Marc, and Michael B. Hall. "Generalized Molecular Orbital Theory II." Journal of Physical Chemistry A 101, no. 37 (September 1997): 6936–44. http://dx.doi.org/10.1021/jp963953l.

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49

Murrell, J. N. "Ab initio molecular orbital theory." Journal of Organometallic Chemistry 309, no. 3 (August 1986): C72—C73. http://dx.doi.org/10.1016/s0022-328x(00)99651-7.

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50

Olcari, Luigi. "Ab initio molecular orbital theory." Inorganica Chimica Acta 119, no. 2 (September 1986): 234. http://dx.doi.org/10.1016/s0020-1693(00)84345-5.

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