INDO Parameters Research Articles

Benchmarking Semiempirical Methods To Compute Electrochemical Formal Potentials.

Computational methods to predict and tune electrochemical redox potentials are important for the development of energy technologies. Here, we benchmark several semiempirical models to compute reduction potentials of organic molecules, comparing approaches based on (1) energy differences between the S0 and one-electron-reduced D0 states of the isolated molecules and (2) an orbital energy shift approach based on tuning the charge-transfer triplet energy of the Ag20-molecule complex; the second model enables explicit modeling of electrode-molecule interactions. For molecules in solution, the two models yield nearly identical results. Both PM7 and PM6 predict formal potentials with only a slight loss of accuracy compared to standard density functional theory models, and the results are robust across several choices of geometries and implicit solvent models. PM6 and PM7 show dramatically improved accuracy over older semiempirical Hamiltonians (MNDO, AM1, PM3, and INDO/S). However, our recently developed INDO parameters model the electronic properties of our Ag20 model electrode much more accurately than does PM7. These results demonstrate the need for further development of semiempirical models to accurately model molecules on surfaces.

A method for calculations of the electronic spectra of transition metal compounds

A new method for the calculations of the electronic structure and spectra of transition metal compounds is based on the CI approach with restrictions imposed on the occupancies of the groups of molecular orbitals. Proper selection of the active space composition allows account of correlation and orbital relaxation effects with the use of a CI matrix of moderate size. A new parametrization scheme for the atomic INDO parameters for transition elements is proposed. Solvent effects are treated in the framework of a simple parametric scheme.

INDO parameters for the elements of the I and II transition rows

AbstractIt is shown that with the use of published one‐center INDO parameters for transition metals M, it is not possible to reproduce experimental relative energies of the electronic states of M, M+, and M2+ accurately enough. Two new sets of INDO parameters for the elements of the I and II transition rows are developed. These parameters are obtained by the method which ensures that the calculated energy differences between atomic electron states are in agreement with the experimental data. The results of some molecular test calculations are presented. © 1995 by John Wiley & Sons, Inc.

Indo parameters for the first-and second-row transition metals

A system of INDO parameters F0(ij) and Uii for the first-and second-row transition metals is proposed. The system correctly reproduces the energies of the lowest terms of dn, dn−1s, dn−2s2, dn−1p, and dn−2sp configurations of M0 atoms and M1+ ions. The parameters are estimated from spectroscopic values of energies of the terms and Fk(ij) and Gk(ij) parameters.

INDO/GIAO calculations of 13C, 15N and 17O NMR chemical shifts in some organo‐iron complexes

AbstractIn this paper, INDO perturbation theory has been extended to calculate the NMR chemical shifts of transition metal compounds. The nitrogen and oxygen INDO parameters have been refined by using a set of nitrogen and oxygen containing compounds to minimize the differences between calculated and experimental 13C, 15N, and 17O shielding constants. These refined parameters, together with optimally selected iron INDO parameters, were used to evaluate the 13C chemical shifts of three iron complexes (C5H5)Fe(CO)2CN, (C5H4CHO)2Fe2, and (C5H4CH2OH)2Fe. The calculated 13C, 15N and 17O shielding constants were fairly in agreement with experimental results. In addition, a good linear relationship between the calculated [diamagnetic shielding constants σd(M) of 13C, 15N and 17O nuclei and the net charge ρ (M) of these atoms was noticed.

13C chemical shifts in series of adamantane and norbornane derivatives. INDO calculations

13C α-substituent chemical shift (α-SCS) calculations were performed with GIAO's and at the INDO-FPT and London levels of approximation for 1- and 2-substituted adamantanes, and 1-, 7-, exo 2- and endo 2-substituted norbornanes. A good overall agreement between calculated and observed α-SCS was revealed when a modified set of INDO parameters for the fluorine, oxygen and nitrogen electronegative atoms is used. α-SCS are shown to correlate with the local calculated charge, and in addition, to be determined almost entirely by the local paramagnetic term, which in turn depends on the atomic charge. 13C substituent chemical shifts as well as the corresponding Δ q atomic charges are also observed to be directly related to the group electronegativity of the α-substituent, hence emphasizing the importance of the σ inductive mechanism in the transmission of the α-substituent effect. SCS values at positions other than α in the series of substituted adamantanes and norbornanes are generally not well predicted theoretically.

Calculation of NMR chemical shifts. 7. Gauge-invariant INDO method

A gauge-invariant INDO method based on the coupled Hartree-Fuck perturbation theory is presented and applied to the calculation of 1H and 13C chemical shifts of hydrocarbons including ring compounds. Invariance of the diamagnetic and paramagnetic shieldings with respect to displacement of the coordinate origin is discussed. Comparison between calculated and experimental results exhibits fairly good agreement, provided that the INDO parameters of Ellis et al. (J. Am. Chem. Soc. 94, 4069 (1972)) are used with the inclusion of all multicenter one-electron integrals.

Application of molecular models to electronic structure calculations of defects in oxide crystals. I. Parametrization of the modified INDO method

A modified calculation scheme of the INDO method is applied for calculating the electronic structure of perfect and imperfect oxide crystals. In order to obtain a flexible scheme permitting reliable calculation of both the electronic structure and the defect conformations, the INDO parameters for H, Li, Mg, Si, O are fitted directly to reproduce one-electron energies as well as the vicinity of the potential energy curve minima for a series of diatomic molecules and the electronic structure of MgO and β-crystoballite form of SiO2. The method is tested on the Li2SiO3 crystal calculated within the framework of the large unit cell model.

Some indo parameterised MO calculations of cobalt nuclear shielding in some diamagnetic hexacoordinate cobalt(III) complexes

Some 59Co nuclear shieldings are calculated by means of Pople's model in conjunction with INDO parameters. Reasonable agreement between calculated and observed 59Co chemical shifts, relative to [Co(CN) 6] -, is reported. The interpretation of the chemical shift differences in terms of variations in ( r −3) 3d and Δ E is examined.

Calculations of some 1J(SiC) and 1J(SiF) values

AbstractSome calculations of 1J(SiC) and 1J(SiF) are performed by self‐consistent perturbation theory employing standard INDO parameters. 1J(SiC) is dominated by the contact interaction, whereas the opposite sign for 1J(SiF) is due to a large orbital interaction. The 1J(SiC) data are satisfactorily reproduced by calculations employing an sp basis set, whereas the inclusion of silicon 3d orbitals provides a more reasonable account of 1J(SiF).

Some INDO calculations of 1J(PN) values

AbstractSelf consistent perturbation theory calculations of 1J(PN) are performed using INDO parameters. The change in sign of the coupling upon passing from tri‐ to penta‐valent phosphorus arises from the influence of the phosphorus lone‐pair electrons. The observed coupling trends are reproduced by the variation in the contact contribution which, in turn, depends largely upon the s character of the lone‐pair electrons on the coupled nuclei. There appears to be no significant role played by the phosphorus d orbitals in the couplings considered.

Substituent effects on one‐bond 15N13C couplings in N,N‐dimethylanilines and nitrobenzenes. Effect of steric inhibition of conjugation

AbstractThe 1J(15N13C) values for a series of ring‐substituted N,N‐dimethylaniline‐15N derivatives and a series of nitrobenzene‐15N derivatives were measured from the 13C spectra. In the nitrobenzenes, small changes in 1J(15N13C) are attributed to the inductive effect of the substituents, since steric inhibition of conjugation has little effect on the magnitude of the coupling. In contrast, steric inhibition of nitrogen lone‐pair delocalization in N,N‐dimethylaniline derivatives markedly reduces the value of 1J(15N13C). Theoretical calculations of 1J(15N13C) values for the two series of compounds were made using standard INDO parameters and a ‘sum‐over‐states’ perturbation approach. Fair agreement between the calculated and experimental values is found.

INDO calculations of the solvent dependence of some spin–spin couplings of fluorocarbons

AbstractThe results of some SCPT and SOS calculations of 1J(CH), 1J(FC), 2J(FH), 3J(FH), 3J(FF) and 1J(CC) in a variety of solvents are reported. The calculations employ the solvaton model and INDO parameters. In almost all cases the coupling is predicted to increase as the dielectric constant of the solvent increases, the exception being 3J(FH)cis in trifluoroethylene which is supported by experimental results.

Some calculations of solvent effects on one bond NC spin–spin couplings

AbstractThe solvaton model, incorporating INDO parameters and commonly encountered perturbation procedures, is employed to obtain the variation of 1J(N≡C) as a function of the dielectric of the medium (ϵ) for some cyanides and isocyanides. In all cases considered 1J(N≡C) is predicted to become increasingly negative as ϵ increases. Changes of up to 2 Hz in 1J(N≡C) are expected, with the isocyanides being more sensitive than the cyanides to a change in ϵ.

Semiempirical Calculations of Defect Properties in LiF Crystal

AbstractTo obtain the electronic structure of both, perfect and imperfect ionic crystals the standard calculation scheme of the INDO semiempirical method is modified in order to consider the interaction of valence electrons with ionic cores more accurately than it has been done so far. The INDO parameters are optimized to reproduce a number of experimentally observed properties of a perfect LiF crystal. The parameters derived permit to reproduce quite well the distinctive properties of free F02, F−2, LiF molecules which is necessary for reliable calculations of the properties of intrinsic hole defects.

A pseudoatom molecular orbital approach to substituent effects in organic Compounds. III. HH coupling constants in substituted ethylenes, ethanes, and benzenes

The FP/INDO molecular orbital method is employed in the investigation of substituent effects on HH coupling constants in substituted ethanes, ethylenes, and benzenes. Substituent effects are simulated by varying the ( 1 2 )(I + A) INDO parameters on two different types of “pseudoatoms,” one essentially a pseudo-hydrogen and the other involving 2 s and 2 p orbitals on two centers. Using this technique, the effective separation of inductive, π, and hyperconjugative effects is obtained. General agreement is found with predictions of previous simpler MO theories of coupling constants and with experimental relationships.

Influence of the INDO parameterization on the indirect spin–spin coupling constants as calculated by the FPT INDO method

AbstractAlterations have been introduced in the semi‐empirical INDO parameters in order to study their influence on the Fermi contact term of the indirect spin–spin coupling constants as calculated by the finite perturbation theory (FPT). For this purpose a set of molecules containing hydrogen, carbon and/or fluorine has been selected. In general, most coupling constants are found to be much more sensitive than other molecular properties to small changes in the INDO parameters. This sensitivity depends strongly on the particular calculated coupling constant. In most cases the uncertainty in the INDO parameters leads to uncertainties in the coupling constants which are much greater than their experimental errors.

A note on the calculations of spin–spin coupling constants involving carbon

AbstractSum‐over‐states perturbation and self‐consistent perturbation calculations of nJ(CC) using standard INDO parameters are discussed. Calculated values of 1J(OC) for acetone are reported. In general it seems that the sum‐over‐states calculations are the more reliable. The importance of including non‐contact contributions in the calculation of couplings between carbon and nuclei with larger values of 〈r−3〉 is stressed.

Calculations of the Solvent Effects on Some Nitrogen Chemical Shifts

Abstract Nitrogen screening constants are calculated by the sum-over-states method using INDO/S parameters and by the finite perturbation procedure employing INDO parameters. The solvaton model is employed to describe changes in nuclear screening as a function of the dielectric constant of the medium. The calculated variations of nitrogen screening are in reasonable agreement with the available experimental data. The effects on screening of hydrogen bonding are included in the sum-over-states calculations by means of dimer models.

13C NMR: Substituent effects on one‐bond 15N13C coupling constants in anilines and anilinium ions

Abstract1J(15N13C) values obtained from FT 13C NMR spectra were measured for a number of 15N‐enriched aniline derivatives and are found to exhibit varying degrees of dependence on the nature of the ring substituent. Theoretical calculations of 1J(15N13C) values for representative members of the systems examined were made using INDO parameters and a ‘sum‐over‐states’ perturbation approach. The calculated coupling constants are generally in fair agreement with experimental values when the integral products SN2(o)SC2(o) and (r−3)N(r−3)C have values of 34.437 au−6 and 2.770 au−6, respectively.