INDO Method Research Articles

Crystal lattice energy of ammonium and methanaminium chlorides

The fraction of crystal lattice energy of ammonium and methanaminium chlorides caused by electrostatic interactions has been evaluated on the basis of modified Coulomb equation for infinite number of interacting charges using available crystallographic information and estimating charge distribution for cations by MNDO and INDO methods. The evaluated characteristics compare well with experimentally derived crystal lattice energies particularly with respect to the observed trends of both quantities on the degree of substitution.

Dependence on saccharide conformation of the one-bond and three-bond carbonproton coupling constants

A theoretical study is presented of the dependence on conformation of 1 J C,H and 3 J C,H values in model compounds related to glycosides. Calculated J values for dimethoxymethane and 2-methoxytetrahydropyran are based on the FPT formulation in the semiempirical INDO method. The configuration at the anomeric carbon affects the 1 J C;H value, and the 1 J C,H and 3 J C,H values vary characteristically with dihedral angle about the carbonoxygen bond. The agreement of the calculated and experimental values is satisfactory, especially for the 3 J C,H values.

Modification of the INDO Calculation Scheme and Parametrization for Ionic Crystals

AbstractA new parametrization of the semiempirical quantum‐chemical INDO method is proposed for the study of the electronic structure of a wide class of perfect and defective ionic insulating crystals. The applicability of the “cut‐off function” concept for the calculations of exchange interactions in the large unit cell (LUC) model is also briefly discussed. Both, the proposed calculation scheme and the parametrization are tested on a number of molecules, ionic crystals (LiH, LiF, LiCl, KCl, MgO, K2SO4), and (100) crystal surfaces of LiF, KCl, MgO.

John Pople: the CNDO and INDO methods

John Pople: the CNDO and INDO methods

Models of electronic defects and self-trapped excitons in Li2O

The semi-empirical INDO method and the embedded-molecular-cluster model have been applied to calculate the atomic structures and electronic transition energies of the F+, F and F2 centres in Li2O and to simulate the self-trapping process of a triplet exciton. Using the parameters of the Slater-type floating orbitals adjusted to the experimental transition energy (4.13 eV) and hyperfine splitting parameters of the F+ centre, the transition energies of the F and F2 centres were obtained to be 4.82 eV and 3.31 eV, respectively. The lattice relaxation accompanied by formation of a triplet exciton and by two neighbouring triplet excitons are also simulated. The results indicate that a triplet exciton is self-trapped by a shift of an oxygen ion by 0.34 AA along a (100) direction, while defect formation as a consequence of the relaxation of a triplet exciton is very improbable. The authors found that two excitons at the nearest neighbour relax into a more stable relaxed state including an O2- bond, and further to a vacancy-interstitial pair. The results of the simulation were compared with experimental observation of the effects of neutron irradiation and of heavy-ion irradiation of Li2O.

An approximate treatment of Kα X-ray emission chemical shifts in sulfur-containing molecules and ions

Sulfur Kα 1,2 X-ray transitions are calculated for a series of systems using the equivalent-cores approximation in which sulfur with a core hole is replaced by a Cl + ion. Charge densities on such chlorine atoms are evaluated using the INDO method and correlated with experimental transition energies. The position of Kα 1,2 lines which cannot be resolved experimentally are predicted. A qualitative explanation of valence orbital penetration into the atomic core and the resulting effects on X-ray spectra is presented.

Geometry optimization of Zn1− xMnxS structures by SCF CNDO and INDO methods

The clustering of Mn ions in the ZnS host lattice is studied by CNDO and INDO methods. The clustered structures were found to be of much lower energy than those with uniform distributions. This effect was explained in terms of the electron delocalization and orbital sharing which are more favoured in the low symmetry clustered compounds. A new interpretation of the spectral bands observed at high Mn concentrations is put forward.

Geometry Optimization in Molecular Structure Calculations: Vinylcylopropane and Vinyloxirane

Abstract The necessity of geometry optimization within the framework of a particular molecular orbital technique is demonstrated using the INDO and EHMO semiempirical methods. The difficulty of finding the global minimum and the proper choice of technique is also discussed. The choice of molecules demonstrates that structure optimization can completely reverse the prediction of which conformer has the lowest energy.

Investigation of conformations and electronic structure of diphenylamine and the diphenylaminyl radical by means of MNDO and INDO methods

Investigation of conformations and electronic structure of diphenylamine and the diphenylaminyl radical by means of MNDO and INDO methods

Ab initio and INDO SCF MO study of monosubstituted hydrazyl radicals

The unrestricted Hartree-Fock ab initio SCF MO method was applied to the monosubstituted hydrazyl radical XN-NH 2 (X = H,CH 3,HC(O),CH 3C(O) or C 6H 5) and [XNH-NH 2] .+ (X = H or CH 3). The optimized geometrical parameters for these radicals obtained via analytical gradient procedures are reported, and the isotropic hyperfine splitting constants calculated both directly from the ab initio wavefunctions and also corrected by employing a recently proposed spin annihilation method. In addition, the INDO method was used in conjunction with these same optimized geometrical parameters to calculate a further set of values for these isotropic hyperfine splitting constants. In general, satisfactory agreement was obtained between the corrected ab initio derived splittings, those from INDO, and experimentally measured values.

Effect of the orientation of an α‐substituent on vicinal 13C–;1H spin–spin coupling constants

AbstractThe magnitude of the NMR spin‐spin coupling constant, 3J(CH), between a vicinal 13C–1H pair depends, inter alia, on the value of the torsion angle ΦCH(13CCCH) and is influenced by the presence of an electronegative substituent located on the coupling 13C nucleus. The form and magnitude of the effect of the orientation ΨXC of such an α‐substituent were examined. The coupling constant between C‐1 and a hydrogen atom located on C‐3 in a series of α‐substituted propanes were studied by means of the semi‐empirical INDO method. In the calculations both Φ and Ψ(X13CCC) were systematically varied in steps of 30°. These calculations reveal that the variation of Ψ at a constant Φ has a pronounced effect on the calculated coupling constant Jcalc. The magnitude of this effect is shown to be strongly dependent on the electronegativity χ of the α‐substituent. Thus, it is shown that Jcalc depends on Φ and Ψ, in addition to χ. The resulting set of two‐dimensional Karplus‐type surfaces can be described by an equation that contains only nine adjustable parameters. Measurement of 3J(CH) in cis‐ and trans‐2,2,6,6‐tetradeuterio‐4‐tert‐butylcyclohexanol confirmed some of the theoretical predictions. In the cis compound (ΦCH = 180°, ΨOC = 60°) 3J(C‐1,H‐3eq) is 7.1 Hz, whereas in the trans compound (ΦCH = 180°, ΨOC = 180°) 3J(CH) equals 10.4 Hz, in qualitative agreement with the INDO calculations.

Molecular and electronic structure of M(2,4-dithiobiuret) 2 complexes (M = Ni 2+, Pd 2+ Pt 2+) by a theoretically improved indo method

Using a modified LCAO MO INDO CI method, the molecular and electronic structure of Ni(II), Pd(II), and Pt(II) complexes with 2,4-dithiobiuret (DTB) was studied. The results of the conformational analysis show that the most stable conformers are those with distortion angles of 0°, 5° and 20° for nickel, palladium and platinum complexes, respectively. The existence of two minima for the total molecular energy of nickel and platinum compounds describe their occurrence as different conformers in the solid state and in solution. Stabilization of the complex conformers was found to be mainly dependent on the metal-sulphur electrostatic interaction. The calculated excitation energies and oscillator strengths are in very good agreement with the experimental data.

Detection of nitrosofuran anion radicals in the electrochemical reduction of 5-nitrofuran. EPR investigations and quantum-chemical calculations

Previously unknown radicals that are associated with the 5-N-furylhydroxylamine-5-nitrosofuran redox system were detected by EPR spectroscopy in the electrochemical reduction of 5-nitrofuran. The electron structures of the free-radical products of the reduction of 5-nitrofuran were calculated by the INDO method. On the basis of the hyperfine structures (hfs) of the EPR spectra and the results of quantum-chemical calculations it was concluded that 5-nitrosofuran anion radicals and the nitrosofuran dimer were recorded.

Pentakis(triphenylphosphine oxide)chlorolanthanide bis(feric tetrachloride) complexes

Twelve new complexes with the general formula [(Ph 3P=O) 5LnCl][FeCI 4] 2 where Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Y were synthesized. The X-ray diffraction crystal structural analysis of [(Ph 3P=O) 5LaCl] [FeCl 4] 2 showed that the [(Ph 3P=O) 5LaCl] 2+ cation was of six coordinated distorted octahedral geometry and the [FeCl 4] − anion was of tetrahedral geometry. The INDO method study revealed that the coordination of PO groups to the lanthanide made the LnCl bond more reactive than that in LnCl 3, so that Lewis acids, such as FeCl 3, could abstract chloride to give the title complexes.

Coordination of neighboring CH bond to transition metal center: III. Study on localized molecular orbitals of the binucleate ion [Fe2(CH3)(CO)(Ph2PCH2PPh2)Cp2

A localized INDO method was used to calculate the ion [Fe2 (CH3) (CO) (Ph2PCH2PPh2)-Cp2]+. Based on the analysis of the localized molecular orbitals (LMO), bond orders and contour maps, it was pointed out that the LMO no. 20 corresponds to the coordination of C(1)—H(1) σ bond to Fe(2) atom. Non occurrence of metal-metal bond between Fe(1) and Fe(2) atoms was found and the covalence of irons was numerated, which coincides with the value in ref 17.

Theoretical INDO Investigation of the Electronic Structure of Aluminium Clusters

AbstractA modified version of the semiempirical INDO method is developed and applied to the study of the electronic properties of Al clusters. The method is able to reproduce in a satisfactory manner the basic features of low‐nuclearity Al clusters as determined by ab initio calculations and can be considered reliable for the study of larger aggregates. In addition, the method can be adopted in a preliminary search of the geometry–energy hypersurface in order to select a few “probable” topologies to be investigated in more detail with rigorous quantum chemical approaches.

Quantum-chemical analysis of acid-base properties of metal complexes of azaporphyrins by the INDO method

Quantum-chemical analysis of acid-base properties of metal complexes of azaporphyrins by the INDO method

Medium effects on the molecular electronic structure: Part 2. The application of the theory of medium effects in the framework of the CNDO and INDO methods

This paper describes a method for the application of the self-consistent reaction-field (SCRF) theory developed in a previous paper (Hoshi ., J. Chem. Phys. 87, 1987) 1107). The theory is combined with the CNDO and INDO molecular orbital methods. The solvent-induced changes in the Helmholtz free energy and in the dipole moments of solute molecules are calculated, and the results are compared with the corresponding ab initio data in the literature. Some approximations are introduced for the estimation of the electrostatic potential and its gradient, created by the charge distribution of a solute molecule. In order to take into account a contribution of the differential overlap between 2 s and 2 p atomic orbitals in first row atoms, point dipoles are placed at each atomic center. It is shown that with this approximation the CNDO and INDO calculations reproduce the reference data well. Finally, the characteristics of the present SCRF theory are discussed by comparison with another semi-empirical reaction-field model, called the “solvaton” model.

Cluster model approach to chemisorption on aluminum: Surface relaxation effects on the interaction of atomic oxygen with the Al(111) surface

The chemisorption of atomic oxygen on Al clusters, sections of the Al(111) surface containing up to 49 Al atoms, has been investigated by means of a modified version of the INDO method. The study has shown that the bonding between oxygen and the Al(111) surface is very strong and of basically local nature. The interaction proceeds through three steps: the formation of a chemisorbed overlayer, the overcoming of an energy barrier, and the incorporation of the oxygen atom in cavities below the surface. The reconstruction of the metal surface occurring when oxygen penetrates the top layer of the cluster greatly reduces the energy barrier to surface penetration.

15N and 13C NMR chemical shift calculations for the sequence analysis of Bombyx mori silk fibroin protein with FPT INDO method

The 15N and carbonyl 13C NMR chemical shifts of the Gly residue were calculated theoretically with FPT INDO method for the sequence model compounds, of Bombyx mori silk fibroin protein, Acetyl-Ala-Gly-NHMe, Acetyl-Ser-Gly-NHMe, Acetyl-Gly-Ala-NHMe and Acetyl-Gly-Ser-NHMe, in order to examine the origin of the 15N and carbonyl NMR sequence splittings previously observed. The order of the observed sequence splittings of B. mori silk fibroin was reproduced by the calculation although the width of the splittings was small.