Determination of one-centre core integrals from the average energies of atomic configurations

One-center core integrals for valence orbitals are determined from the experimental average energies of neutral atomic configurations from Li through Zn. These values are compared with those estimated from CNDO /1, “INDO /1”, CNDO /2, “INDO /2” and with theoretical values calculated from a pseudo-potential method. The agreement is good between values obtained from neutral atoms and from the psuedo-potential calculation except for the 3d orbitals of the transition elements where the theoretically calculated integrals over single ξ functions are not realistic. These two methods reproduce both term and average configuration energies for the first two rows of atoms; the semiempirical method reliably reproduces them for the third row. The CNDO /1 and INDO /1 methods underestimate atomic energies, while the CNDO /2 and INDO /2 procedures fail rather poorly. The propriety of using core integrals estimated semiempirically in molecular orbital calculations is discussed.     

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.     

Theoretical research of isomerization mechanisms from cis to trans form in polyacetylene

The characteristics of photo, thermal and doping isomerizations of polyacetylene were discussed. A new biradical mechanism for photo and thermal isomerizations is proposed, which is consistent with the ESR results. The CNDO/2 and INDO molecular orbital calculation results show that the mechanism is energetically the most favorable. The reliability of applying general semi-empirical MO methods in polymers is estimated and showed to be valuable in predicting properties.     

Semiempirical calculation of electronic spectra of organic compounds by using the improved method of new-γ electron repulsion integral. Part 2. Polycyclic aromatic hydrocarbons (PAHs)

Excitation energies of 123 polycyclic aromatic hydrocarbons were calculated by incorporating the improved method of new-γ for the two-center electron repulsion integral into two semiempirical molecular orbital methods (CNDO/S and INDO/S). This variable method well reproduced experimental excitation energies of them. The average error of the improvement is about 0.162 (CNDO/S) or 0.237 eV (INDO/S) though the average error without the improvement is about 0.541 (CNDO/S) or 0.536 eV (INDO/S). The improvement was useful for the calculations of other organic compounds including hetero atoms, such as organic dye.     

Study of the electronic energy band structure of polyethylene using MINDO/3

The electronic structure of polyethylene has been calculated using crystal orbital theory and the latest version (MINDO/3) of the MINDO semi-empirical SCF MO method. The results are in better agreement with the observed photoelectron spectrum than those given by an analogous calculation using MINDO/2, which in turn has been shown superior to treatments based on EHT, CNDO, INDO, or ab initio SCF procedures.     

Calculation of raman intensities by a modified cndo/2/indo method

Line intensities in Raman spectra determined by means of a modified CNDO/2 and a modified INDO method [1,2] give perturbation terms which are inserted into the Hartree—Fock operator used in the CNDO/2 and INDO theory [3, 4] to yield the induced dipole moment as a function of the normal co-ordinate Q, from which the polarizability change upon Q is obtained. The results for ethylene, tetrafluoroethylene, tetrachloroethylene, dichloromethane and phosgene are discussed. Calculated intensities agree well with experimental intensities obtained from Raman spectra.     

Non-empirical SCF studies of the ring and open forms of ozone

Non-empirical SCF calculations have been used to investigate the relative stabilities of the open and closed forms of ozone. In these studies several different sized basis sets have been employed, the best basis set being at about the level of a double-zeta set plus d-polarization functions. In contrast to the predictions of the CNDO/2, INDO and MINDO methods, the non-empirical SCF studies correctly predict that the open form of ozone is more stable. Thus these results show that the area of deficiency in the CNDO/2, INDO and MINDO results for this system is not in the SCF approximation.     

On methods for converging self-consistent-field iterations

A method using linear combinations of successive eigenvectors based on energy minimization is presented for converging self-consistent-field iterations. It is applied to a number of divergent or poorly convergent examples in semi-empirical CNDO, INDO, and ab initio STO-3G calculations. The CNDO/2 results are compared with those obtained by the level-shifting and damping techniques.     

Evaluation of EFG parameters in XO−3 ions (XCl,Br,I) by CNDO/2 and indo methods

One can not apply the conventional point charge model to evaluate the EFG parameters at the halogen site in chlorates, bromates and iodates since, in XO^?₃ ions (XCl,Br,I), the halogen atom is covalently bonded to the oxygens of the group and the effect of the cation on EFG is negligible. Therefore molecular orbital calculations by both CNDO/2 and INDO methods have been attempted to evaluate the EFG parameters. The currently available program (ref.1) for CNDO/2 and INDO methods has been extended to III and IV row elements using Hase and Schweig (ref.2) and Deb and Coulson (ref.3) parameters. The EFG parameters obtained from population density matrix (ref.4) from these two methods have been compared with the experimental data wherever available. It has been concluded that CNDO/2 method is better suited for the determination of EFG parameters in XO^?₃ ions compared to INDO method. The reason for this is discussed.     

CNDO/2 and INDO calculations of a reaction pathway for the sigmatropic [1, 5] H-shift in cyclopentadiene

CNDO/2 and INDO calculations have been carried out in order to construct a suitable model for the activated complex during the reaction. In this reaction model the migrating hydrogen atom moves along an edge of the cyclopentadiene ring. An analysis of this situation suggests a partial electron transfer from the migrating hydrogen to the nascent cyclopentadienyl system. This charge transfer is discussed in terms of aromaticity. The calculated activation enthalpies are 10 kcal/mole (CNDO/2) and 17 kcal/mole (INDO), whereas the experimental value is ca. 24 kcal/mole [1].     

A CNDO/INDO crystal orbital model for transition metal polymers of the 3d series—basis equations

The crystal orbital formalism in the tight-binding approximation is combined with a recently developed CNDO/INDO model for transition metal species of the 3d series in order to allow band structure calculations on the Hartree-Fock (HF) SCF level for one-dimensional (1D) chains with organometallic unit cells. The band structure approach based on the CNDO and INDO approximation can be used for any atom combination up to bromine under the inclusion of the 3d series. The matrix elements for the tight-binding Hamiltonian are derived for an improved CNDO and INDO framework. The total energy of the 1D chain is partitioned into one-center contributions and into two-center increments of the intracell and intercell type. Semiempirical band structure calculations on simple model systems are compared with available ab initio data of high quality.     

Quantum chemical calculations of fluoroethylene molecules by the CNDO and INDO methods

Conclusions A quantum chemical calculation of seven fluoroethylene molecules and two fluorochloroethylene molecules and two fluorochloroethylene molecules by the CNDO and INDO methods has made it possible to explain the experimentally observed change in reactivity and direction of addition reactions at the double bond. The data of a calculation of the relative stability of various isomers also agree with the experimental results.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2199–2202, October, 1973.     

Approximate SCF CI calculation of excited state geometries of phenol,aniline, para-fluorophenol and para-fluoroaniline

The CNDO/s method has been used to study the electronic structure, spectra, geometry and rotational constants in the ground and the first excited singlet states of phenol, aniline, para-fluorophenol and para-fluoroaniline. The ground state geometry has also been studied using CNDO/2 and INDO methods. Calculated bond length changes following the electronic excitation have been compared with experimental results and ambiguities present in the latter have been resolved.     

All-valence MO study of hydrogen bonding in water

Theoretical hydrogen bond energies and proton barriers for water dimer and trimer calculated by semiempirical all-valence MO methods have been compared. The results of CNDO/2 and INDO calculations are more adequate than those obtained by the MINDO/1 approach.     

Virtual orbital transformation prior to configuration interaction with localized orbitals

A virtual orbital transformation is proposed involving pairing of localized occupied orbitals with virtual orbitals. The virtual orbitals are transformed so that each virtual orbital is as “close” as possible to its occupied counterpart, where closeness is the inverse of the particular definition of localization. The appropriate transformation is derived for the special case of Foster–Boys localization, and an illustrative CNDO /2 calculation on HNO is presented. INDO CI results on the series N₂, CO, BF indicate that use of this transformation may reduce the number of energetically significant configurations.     

Calculation of vertical excitation energies of closed-shell molecules in the CNDO and INDO approximations

The Green's function method for the calculation of vertical excitation energies is adapted to the CNDO and INDO approximations by introducing an effective interaction into the irreducible vertex part. The computational scheme is explicitly developed for closed-shell molecules and applied to H₂O, H₂CO, HCOOH, HCONH₂.     

在不加对称性限制的条件下采用不同的半经验方法研究酞菁的电荷分布和几何构型（英文）

在不加对称性限制的条件下采用不同的半经验方法CNDO,INDO,MINDO/3,MNDO和Pm3对自由酞菁(H2Pc)进行几何构型最优化和电荷密度布居分析,并将所得结果与Am1方法以及X射线衍射和中子衍射数据的数据进行比较.结果表明只有从INDO方法得到的是桥式构型,而从CNDO, MINDO/3, MNDO,Am1, Pm3方法得到的都是键式构型.除INDO之外所有的这几种方法都对先前报道的几何构型扭曲给出进一步的支持证据.新近建立的半经验方法如MNDO,An1,Pm3等看起来更适合于用来研究大分子如酞菁及其类似物的几何构型扭曲和电荷分布极化等问题.     

AN EXTENDED SEMI-EMPIRICAL MOLECULAR ORBITAL STUDY OF THE * EXCITED STATES OF NUCLEIC ACID BASES

Spectroscopic CNDO/S and INDO/S calculations of the * spectra of the nucleic acid bases uracil, cytosine, adenine and guanine were performed. Oscillator strengths, polarizations and transition densities are displayed for transitions to 140 nm using several parameter sets and demonstrating the effect of doubly excited configurations. Inclusion of near-neighbor off-diagonal transition density elements greatly assists in making state correlations and assignments. Interesting effects regarding electron repulsion parameterization are noted. The results are compared with recently reported experimental results and several serious points of disagreement are noted.     

Calculations of the isotropic hyperfine coupling constants in free radicals

For a number of free radicals the results of non-empirical (ab initio) and semi-empirical (INDO, DEPAC, CNDO/SP) calculations of the isotropic hyperfine coupling constants are compared.