Application of SINDO1 to silicon,aluminum, and magnesium compounds

SINDO1 calculations are presented for ground state geometries, heats of formation, ionization potentials and dipole moments of silicon, aluminum and magnesium compounds. These calculations are based on a new parametrization of SINDO1 for second-row elements. Important features are the inclusion of 3d orbitals and the explicit evaluation of zero point energies. A comparison with MNDO data is presented.     

Application of SINDO1 to sulphur compounds

SINDO1 calculations are presented for ground state geometries, heats of formation, ionization potentials and dipole moments. These calculations are based on a new parametrization of SINDO1 for second-row elements which features inclusion of 3d orbitals and zero point energies. The comparison shows an improvement over MNDO, especially for hypervalent sulphur compounds.     

Application of SINDO1 to phosphorus compounds

SINDO1 calculations are presented for ground state geometries, heats of formation, ionization potentials and dipole moments. These calculations are based on a new parametrization of SINDO1 for second-row elements which features inclusion of 3d orbitals and zero point energies. The comparison shows an improvement over MNDO, especially for hypervalent phosphorus compounds.     

Application of SINDO1 to chlorine and sodium compounds

SINDO1 calculations are presented for ground state geometries, heats of formation, ionization potentials and dipole moments of chlorine and sodium compounds. These calculations are based on a new parametrization of SINDO1 for second-row elements which features inclusion of 3d orbitals and zero point energies. The comparison shows a substantial improvement over MNDO in geometries and heats of formation of hypervalent compounds and ionization potentials, whereas other properties are of similar quality.     

MSINDO parameterization for third‐row transition metals

The recently developed MSINDO version of the semiempirical SCF MO method SINDO1 has been parameterized for third‐row transition metals Sc to Zn. The set of reference data used for the previous parameterization of SINDO1 has been substantially increased by incorporating results of recent experiments and first‐principles calculations. A comparison of calculated heats of formation, geometries, ionization potentials, and dipole moments with literature values for more than 200 gas phase molecules is presented. The accuracy of the modified MSINDO version achieved for heats of formation and bond lengths has been considerably improved compared to SINDO1. Small clusters of transition metals and metal oxides were included in the parameterization to ensure accurate results for studies of larger systems. The application of the method to small transition metal complexes that were not included in the parameterization shows that the optimized parameters are transferable to other compounds. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 861–887, 2001     

Cycloreversion reactions for five to seven membered rings

The cycloreversion of the following ring systems was studied: (1) Cyclopentyl anion → allyl anion + ethylene, (2) Cyclohexene → butadiene + ethylene, (3) Cyclohept-4-enyl cation → butadiene + allyl cation. The potential energy surfaces of these reactions were investigated by the semiempirical MO method SINDO1 under inclusion of a 4 × 4 CI. All internal coordinates were varied. We found major differences in the nature and geometry of transition states and intermediates of these reactions. Diradical character is involved only in the fragmentation of the six membered ring.     

Cycloreversion of cyclobutanes

Semiempirical MO calculations with the method SINDO1 were performed to study the potential energy surface of cyclobutane and several substituted cyclobutanes with substituents F, OCH₃ and CN. The reaction pathway with the lowest activation energy leading to two ethylenic fragments is nonconcerted. One carbon bond is broken after symmetric opening of two adjacent bond angles and twisting of the carbon framework. The first transition state is asymmetric and diradicaloid. The reaction proceeds to a diradicaloid, non-zwitterionic intermediate. The second transition state is characterized by bond breaking of the inner carbon-carbon bond. For the unsubstituted case, the barrier for free rotation of the outer methylenic groups was also calculated. In comparison, the unsubstituted reaction is characterized by transition states of almost equal energy, whereas in the substituted reactions the barriers for the second bond breaking are much higher than for the first bond breaking step.     

Comparative studies on the reactivity of molecules by atomic valences

SINDO1 calculations were performed to study the reactivity of molecules with a valence number derived from the density matrix. A comparison of valence numbers was made for selected examples of rotation barriers, substituted strained molecules, radical gas phase reactions, and acid-base reactions. Relations between valence, geometry, and energy changes are discussed.     

Treatment of anions in SINDO1

The SINDO1 method is modified to include the calculation of molecular anions. Two versions of modifications are presented which are based on charge dependent orbital exponents. Calculated heats of formation and electron affinities are much improved compared to the standard version with fixed orbital exponents.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

Fragmentation and isomerization of 1,2-dimethylcyclobutane

The potential surface of 1,2-dimethylcyclobutane is investigated with respect to fragmentation and isomerization by the semiempirical MO method SINDO1. Energy and geometry of eight transition states and four intermediates are determined for the nonconcerted fragmentations under optimization of all internal coordinates. We find that symmetric cleavage ofcis-dimethylcyclobutane is the most favored process leading to fragmentation. Whereas the symmetric elimination involves two different barrier heights, the asymmetric elimination involves only two equal barrier heights. The possibility of isomerization ofcis- totrans- dimethylcyclobutane was also studied and revealed two different barrier heights lower than the corresponding heights for fragmentation.     

On the rotational invariance of the fock equations in indo methods using d functions

The rotational invariance of the Fock equations is investigated. It is demonstrated that the inclusion of d functions requires additional hybrid integrals which do not occur in the original version of INDDO . Calculations are performed with SINDO 1 on binding energies, ionization potentials, and dipole moments to show the differences between the various levels of approximation.     

Consistent parametrization of semiempirical MO methods

The parametrization of semiempirical molecular orbital methods is reviewed. The parametrization procedures are classified in three categories. The newly proposed category of consistency of parameters in a row of elements is applied in SINDO 1 to the Si atom. The calculations on test molecules and silicon clusters demonstrate that significant improvements in accuracy can be obtained in this way. © 1992 John Wiley & Sons, Inc.     

SINDO1 calculations of vibrational frequencies of adsorbed molecules

A scaling procedure is used for the force constants generated by the SINDO 1 method in internal coordinates to achieve better agreement with experimental frequencies of molecules. The procedure is subsequently used to calculate frequency shifts for adsorbed molecules. The results for CO₂ and CO adsorption at NaCl cluster surfaces are in good agreement with experimental data. © 1995 John Wiley & Sons, Inc.     

Extension of SINDO1 to transition metal compounds

The semiempirical MO method SINDO1, originally suitable for first- and second-row atoms, is extended to transition metals from scandium to zinc. The core Hamiltonian elements in a symmetrically orthogonalized atomic orbital (OAO) basis set are modified and the parameters are optimized to reproduce the experimental geometries, heats of formation, and ionization potentials. An application of the method to a selected number of molecules, as well as a comparison between calculated and experimental data is reported.     

The role of 2,3-dimethylene-1, 4-cyclohexadiyl diradical as a reactive intermediate in some rearrangement reactions

Quantum chemical CI calculations with the semiempirical MO method SINDO1 are performed to study the rearrangement reactions of 1,2,6,7-octatetraen, 2,3-dimethylenebicyclo(2.2.0)hexane, 3,4-dimethylene-1,5-hexadiene and bicyclo(4.2.0)octa-1,5-diene. It is shown that the most favorable pathway of each of these six rearrangements involves the 2,3-dimethylene-1,4-cyclohexadiyl diradical as an interceptable intermediate. Two further intermediates, 1,2-divinyl-1-cyclobutene and 1,2-divinylylcyclobutane appear, but the latter with little importance. Energies and geometries of the four reactants resp. products, the three intermediates and twelve transitions states are presented. The mechanism of the rearrangements is discussed.     

Orbital correlation diagrams based on multiconfigurational variation of moments II. Application

A formalism was developed in the multiconfigurational variation of moments (MCM ) framework, which yields physically meaningful orbital energies for occupied and virtual orbitals starting from self-consistent field (SCF ) calculations. This is possible through a skillful distribution of the correlation energy on the orbital energies. The application of this method is demonstrated by SINDO 1 calculations on the dissociation of H₂ and the following symmetry-forbidden reactions: (1) torsion of ethylene; (2) ring opening of (a) cyclobutene, and (b) cyclopropyl cation; (3) cycloreversion of 1, 1-dicyano-2-methoxycyclobutane. The allowed reactions corresponding to 2a and 2b are investigated in the SCF scheme. The energy hypersurfaces are calculated for all reactions and the MO correlation diagrams are presented and discussed.