Application of the NDDO method to transition metal compounds

The NDDO method has been extended to include elements withd-orbitals. A parametrization for the first-row transition metals is given, which has been worked out to describe structural properties of transition metal complexes. Applications of the method to the Jahn-Teller distortions of tetrachloro complexes are presented. The NDDO results are compared with those from CNDO and INDO calculations. It turns out that the NDDO method seems to be the most sensitive among the ZDO procedures.     

NDDO MO calculations: isotropic hyperfine coupling constants and nuclear spin-spin coupling constants

The nonempirical NDDO MO method in its unrestricted form has been used to evaluate isotropic hyperfine coupling constants and nuclear spin-spin coupling constants. Satisfactory agreement with INDO and experimental results is obtained.     

On bridging the gap between the INDO and the NDDO schemes

A series of approximate LCAO-SCF methods intermediate between the INDO and the NDDO schemes is proposed. The suggestion is based upon the decomposition of integrals in multipole-multipole type interactions.     

Semi-empirical all-valence-electron SCF calculations of acidities of cycloalkanes

CNDO/2 calculations of the energy change RHR^–+H⁺ for cycloalkanes give the acidity order: cyclohexane > cyclopentane > cyclobutane > cyclopropane, exactly the reverse of the experimental order. INDO results are similar to CNDO/2. A new method, IRDO, related to NDDO is described. Both of these methods give results differing from the first two but agreement with experiment is still poor.

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Zusammenfassung CNDO/2-Berechnungen der Energieänderung der Reaktion RHR^–+H⁺ für Cycloalkane gibt folgende Reihenfolge für die Acidität: Cyclohexan > Cyclopentan > Cyclobutan > Cyclopropan, was genau der umgekehrten experimentellen Reihenfolge entspricht. INDO Resultate sind den CNDO/2 Resultaten ähnlich. Eine neue Methode, IRDO, die der NDDO verwandt ist, wird vorgeschlagen. Diese Methoden führen zu Resultaten, die sich von denen der beiden ersten unterscheiden, aber die Übereinstimmung mit dem Experiment ist noch immer unbefriedigend.

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Résumé Des calculs CNDO/2 de la variation d'énergie de la réaction RHR^–+H⁺ pour les cycloalkanes donnent l'ordre des acidités à l'inverse de l'ordre experimental: cyclohexane > cyclopentane > cyclobutane > cyclopropane. Les résultats INDO sont semblables à ceux de CNDO/2. Une nouvelle méthode, IRDO, liée à NDDO est décrite. Ces deux méthodes donnent des résultats différents des deux premières, mais l'accord avec l'expérience reste faible.

     

New parametrization scheme for the resonance integrals (Hμν) within the INDO/1 approximation. Main group elements

Among the currently available semiempirical methods, there is still no model equally good for both geometries and spectroscopy. We describe our recent attempt to obtain a set of parameters using the semiempirical INDO/1 model Hamiltonian. We have modified the formula for resonance integrals according to a previous suggestion by Kolb and Thiel for MNDO, and developed a set of parameters for several elements belonging to the first and second rows of the periodic table. This suggested set has been implemented in the latest versions of the ZINDO code and already represents a considerable improvement (relative to Pople's original INDO/1 parametrization) in the calculated geometries. Furthermore, this improved method is shown to be at least competitive with the currently popular NDDO methods. In addition, the results of ionization potentials (calculated at the Koopmans' approximation) and transition energies show that the performance of the INDO/S technique in spectroscopy has been preserved. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 187–201, 2001     

NDDO quantum chemical calculations of molecules. A comparison between the modified version and the AM1 method

Advantages and disadvantages of two approaches to electronic structure calculations of molecules using the NDDO approximation are revealed.     

Semiempirical NDDO calculations with STO-3G and 4-31G basis sets

Possible refinements of semiempirical methods include the use of larger basis sets and of correlated wave functions. These possibilities are investigated in semiempirical NDDO SCF calculations with the STO-3G and 4-31G basis sets, and in correlated calculations at the STO-3G level. The present approach is characterized by the analytical evaluation of all one-center terms and two-electron integrals, and the semiempirical adjustment of the remaining one-electron integrals and the nuclear repulsions. The NDDO SCF results tend to reproduce the correspondingab initio results more closely than experimental data, even if they are parametrized with respect to experiment. The explicit inclusion of electron correlation at the STO-3G level improves the calculated results only slightly.     

Simplified ab-initio calculations for molecular systems

A method is described for reducing a large part of the arithmetic of exact ab-initio SCF molecularorbital calculations based on Slater-type-orbitals without noticeable loss of numerical accuracy. The procedure involves the transformation to Löwdin orthogonalized orbitals and then invoking the NDDO approximation. The three- and four-centre two-electron integrals required are estimated by a truncated Ruedenberg expansion. All one-electron integrals are evaluated exactly. No empirical parameters are employed. Numerical tests on CO, OF₂, O₃ and ONF show that the NDDO approximation is very accurate for Löwdin functions and that the Ruedenberg expansion is arithmetically satisfactory for the SCF MO calculations.     

An extended PCILO method

The perturbative configuration interaction using localized orbitals (the PCILO method) was extended in the way that current limitations to the two-centre bond approach were overcome. The localized molecular orbitals contain an arbitrary number of the basis set components; this follows from the a priori stated localized bonding model of a molecule. The extended PCILO method was formulated for the CNDO, INDO and NDDO Hamiltonian approximations. The configuration interaction was performed using the Rayleigh-Schrödinger many-body perturbation theory with the Møller-Plesset type of Hamiltonian partitioning, similar to that used in the so-called modified PCILO method. Applications to molecules with semi-localized and/or semi-delocalized bonds, as benzene or diborane, are presented.     

Quantum chemical investigation of the molecular structure of some 2,3-dihydro-1,4-diazepines and related molecules

Accurate ab-initio and semi-empirical molecular orbital calculations with full geometry optimization were performed on the various tautomeric forms of some 2,3-dihydro-1,4-diazepines and related molecules. The highly accurate ab-initio calculations at the HF/6–31G7 level with Möller-Plesset Second-Order Perturbation Theory (MP2) refinement clearly established the higher stability of the enamine tautomer of the 1,4-diazepine ring over the di-imine form by 27.786 kJ/mol, whereas the semi-empirical calculations at the NDDO level (AM1 and PM3) predicted comparable energies within reported errors of the two methods. However, both ab-initio and semi-empirical NDDO methods predicted similar geometries in agreement with observed geometrical parameters. The AM1 calculations predicted small energy differences among the three tautomeric forms of 2,3-dihydro-5-methyl 7-phenyl 1,4-diazepine with the more polar enamine tautomer being the more stable tautomer in the half-chair conformation which is likely to predominate in polar media through stabilizing intermolecular solute-solvent interactions.     

Comparison of the RHF,NDDO, and MOM molecular one-electron expectation values calculated using minimum basis sets with Slater,Burns, Clementi,and BLMO exponents

The effect of different exponents, Slater, Burns, Clementi, and Best Limited Molecular Orbital (BLMO ) on the approximate one-electron property expectation values from minimum basis-set calculations is reported for Roothaan–Hartree–Fock (RHF ), neglect of diatomic differential overlap (NDDO ), and maximum overlap method (MOM ) calculations on FH, CO, and LiH.     

An INDO study of the isomerization of aziridinone

The only pathway postulated in the literature for the isomerization of aziridinone (Ia) to iminooxirane (IIIa) involves a planar, open-chain, dipolar intermediate (IIa); however, INDO calculations suggest a possible alternative pathway in which an in-plane bending of the oxygen atom towards the alkyl carbon atom occurs rather than a stretching of the alkyl-nitrogen bond. INDO calculations also suggest that the unknown compound IIIa has the same degree of stability as Ia.     

NDDO MO calculations

The Roby version of the NDDO MO method has been analysed by performing extensive calculations on several molecular systems employing a minimum basis set of STO-3G functions. The effect of using uniform scale factors and those derived from theS-expansion technique, for electron repulsion integrals has also been studied. At the all-electron level, the method, with all its refinements, does not appear promising. The all-valence NDDO MO method after correction byS-expansion, however, yields results which are in good agreement withab initio results. The performance of this scheme is comparable to that of the simplifiedab initio method of Brown and Roby.     

NDDO study of the coordination structure of M(S2CNH2)2 complexes (M = Ni, Cu)

Quantum chemical NDDO calculations were performed with the aim of explaining the differing structures of copper(II) and Ni(II)bis(dithiocarbamate) complexes. Departure from planarity in copper complexes is reproduced by calculations, although the bent angle observed in the crystal is only reproduced when a sulfur atom of the neighbouring complex is included in the model system. An attempt was made to give a qualitative account of the bonding in the two complexes on the basis of the AO picture of the central atom.     

Semiempirical NDDO/MC calculations of the excited states of the chromate ion

A new semiempirical method of calculating the excited states of transition metal complexes is developed. This technique uses the configuration interaction and semiempirical NDDO/MC methods to obtain the ground state of a set of Slater type valence spd-orbitals chosen from the optical spectra of transition metals together with the corresponding core integrals. The method is tested in calculations of the electronically excited states of the chromate ion. Good agreement with the experimental energies of vertical transitions and the results of ab initio calculations is achieved.     

NANOPACK: Parallel codes for semiempirical quantum chemical calculations of large systems in the sp‐ and spd‐basis

A parallel implementation of the conventionally used NDDO (MNDO, AM1, PM3, CLUSTER‐Z1) and modified NDDO‐WF (CLUSTER‐Z2) techniques for semiempirical quantum chemical calculations of large molecular systems in the sp‐ and spd‐basis, respectively, is described. The atom‐pair distribution of data over processors forms the basis of the parallelization. The technological aspects of designing scalable parallel calculations on supercomputers (using ScaLAPACK and MPI libraries) are discussed. The scaling of individual algorithms and the entire package was carried out for model systems with 894, 1920, and 2014 atomic orbitals. The package speed‐up provided by different multiprocessor systems involving a cluster of Intel PIII processors, Alpha‐21264‐processor‐built machine MBC‐1000M, and Cray‐T3E is analyzed. The effect of computer characteristics on the package performance is discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

A comparative study of the structure and bonding of HOO,HOS, HSO,and HSS radicals by CNDO/2 and INDO methods

Equilibrium geometries, force constants, barriers to linearity, charge distributions, dipole moments, and electron spin density of HOO, HOS, HSO, and HSS radicals are calculated by CNDO/2 and INDO methods using respectively the original and some recently introduced scheme of parametrization. Three sets of calculations, namely, CNDO/2(sp), CNDO/2(spd), and INDO, are performed, and the results are compared with the ab initio and experimental values, wherever available. A good agreement is obtained for geometry in the case of CNDO/2 (sp) and INDO calculations. The performance of CNDO/2 (spd) calculations in this regard is quite unreliable. The stretching force constants are considerably overestimated by all the methods, while the bending force constants are in reasonable agreement with the ab initio values. With respect to dipole moments, the CNDO/2 values are in better agreement with the ab initio results than the INDO values. In all the cases, the dipole moment vector directions are in complete disagreement with the ab initio predictions.     

Bond–antibond analysis of internal rotation barriers in glyoxal and related molecules: Where INDO fails

Ab initio and INDO LCBO–MO calculations are carried out on glyoxal, 1,3-butadiene, and acrolein in order to analyze the qualitative failure of INDO -like methods to describe conformation energies in these molecules. Following the method of Brunck and Weinhold for ethanelike systems we identify the principal bond–antibond interactions contributing to the glyoxal barrier, their dependence on dihedral angle and substituent, and their relative magnitudes as calculated by ab initio and INDO SCF–MO theory. We find a gross disparity in the INDO representation of π* interactions which leads to a grossly exaggerated estimate of the stability of gauche conformers in these molecules. These findings appear to have serious implications for the applicability of INDO -like theories to conformational problems in π-bonded molecules, including those of biological interest.     

A theoretical study of nuclear spin coupling constants and hyperfine coupling constants of se-heterocyclics

MO calculations based on the finite perturbation theory in the INDO approximation have been carried out on selenophene, eighteen of its monosubstituted derivatives and benzo (b)selenophene. The calculated nuclear spin coupling constants satisfactorily reproduce signs, magnitudes, internal orders and some trends of the experimental values. Comparison of different ZDO calculations provides information on the relative importance of σ and π pathways for the various coupling constants in selenophene and benzo(b)selenophene. Unrestricted Hartree-Fock calculations at the INDO level have been performed on the radical anions of dibenzoselenophene and 2,1,3-benzoselenadiazole, the phenoselenazine radical cation, the phenoselenazine neutral radical and the phenoselenazine nitroxide. The isotropic hyperfine coupling constants have been found to be generally in satisfactory agreement with experiment.