Complexes with hydrogen bonds by the MNDO/M method

Conclusions The results obtained show that the modified variant of the MNDO method developed in the present work makes it possible to obtain sufficiently reliable and accurate values of the energies of H bonds in neutral and charged complexes and provides perfectly satisfactory estimates of the geometric parameters of H bonds and the activation energies of proton-transfer reactions. Taking into account that MNDO calculations require relatively small expenditures of computer time (approximately 1000 times less than do nonempirical calculations in the 4-31G basis), the MNDO/M method can be used to study chemical reactions in aqueous solutions in the framework of a supermolecular approach, as well as to simulate fairly complicated biochemical processes, for example, the reactions in the active site of an enzyme.Lenin Young Communist League Novosibirsk State University. Novosibirsk Institute of Bioorganic Chemistry, Academy of Sciences of the USSR, Siberian Brach. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 2, pp. 31–37, March–April, 1988.     

MNDO method for calculations of magnesium clusters

A new set of parameters for the magnesium atom has been developed within the MNDO method. In contrast to previously published parameters, the new parameters correctly describe molecules with different chemical natures: magnesium halides, organomagnesium compounds and the recently found small magnesium clusters Mg _n (n=2-8). The average errors in the calculated heats of formation and bond lengths of magnesium compounds, including clusters are: 10.7 kcal/mol and 0.167 Å, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1384–1388, August, 1994.     

Crown compounds for anions. MNDO calculations of complexes of halide anions with cyclic pentameric difluoromethylidenemercury

Molecular and electronic structures of complexes of halide anions with cyclic pentameric difluoromethylidenemercury [CF₂Hg]₅ have been studied by the MNDO method. Calculations have been performed for [L-X]^– halfsandwich complexes and bipyramidal complexes [X-L-X]^2– having a shape of a spinning top (L is the mercury-containing macrocycle; X = F, Cl, Br, or 1). It has been shown that in complexes of both types, halide anions are bonded to the mercury-containing macrocycle via three generalized chemical bonds: one headlightshaped -bond and two two-lobe n-bonds. The complexes studied have been compared with the analogous complexes of the macrocycles containing three mercury atoms. The similarity and differences in the character of the generalized chemical bonds in relation to the size of the cycle have been considered.V. B. Shur, I. A. Tikhonova, F. M. Dolgushin, A. I. Yanovsky, Yu. T. Struchkov, A. Yu. Volkonsky, and E. V. Solodova, Unpublished results.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 44–48, January, 1996.     

A modified MNDO procedure for calculating the heats of formation of organic anions

A modification of the MNDO method is suggested based on the relation ζ_A=ζ_A ⁰(1 + ϰ_AQ_A) for Slater parameters that takes into account the dependence of overlap integrals and the MNDO parameters (expressed via these integrals) on atomic charges Q_A. The core parameters U_μμ include corrections for nonorthogonality of basis functions of atoms in a molecule. For free atoms, the parameters were determined from the condition of reproducible electron affinities. The method is advantageous for calculating the heats of formation of anions, particularly those with the charge concentrated on one atom. Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 3–11, January-February, 1994. Translated by O. Kharlamova     

Efficient method to perform CAP/CI calculations for temporary anions

Electronically metastable states can efficiently be investigted using ??² techniques, such as the complex absorbing potential (CAP) or the stabilization method; but, the study of autodetaching systems is nonetheless far more expensive than the investigation of comparable bound states. The costly step of the ??² methods for resonances involves the repeated diagonalization of a parameterized Hamilton operator, and in this communication we investigate representations of the needed operators in very small basis set consisting of a few eigenstates of the physical Hamiltonian. It is shown that CAP calculations can indeed be performed using a very small eigenstate basis set, whereas basis sets of comparable size are unsuitable for stabilization calculations. Our results allow us to study the frequently employed energy selection procedure in the context of Siegert energies. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 218–226, 2001     

Distribution of electron density and internal rotation in phospha-alkenes according to data from quantum-chemical calculations by the MNDO method

A quantum-chemical investigation of the characteristics of the phosphorus-carbon bond and the internal rotation around it in phospha-alkenes has been carried out in the MNDO approximation. The results of the calculation have been compared with experimental dynamic ¹H NMR data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 734–736, November–December, 1987.     

MNDO calculations of the electronic structure of lead β-diketonates

Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturmoi Khimii, Vol. 35, No. 6, pp. 186–190, November–December, 1994.     

Green's function method for photoelectron spectroscopy calculations based on MNDO and AM1 semiempirical approximations

Irkutsk State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 3, 137–139, May–June, 1989.     

Density functional calculations of structures and ionization energies for heavy group V cluster anions

The structure and electronic structure of heavy-group V cluster anions (Sb, Bi) are calculated with density functional methods within the local spin density approximation (LSDA ). The influence of gradient corrections of the exchange and correlation energy is investigated. The calculated vertical and adiabatic ionization energies are in very good agreement with data from photoelectron spectroscopy (PES ) for Sb, whereas the relatively large deviations for Bi can be reduced by the consideration of relativistic effects in a scalar-relativistic manner. Concerning the structures, a strong similarity to the corresponding P clusters was found. In particular, the negatively charged pentamers are planar rings (with similarities to the aromatic [C₅H₅]^? anion) with especially high ionization energies. © 1995 John Wiley & Sons, Inc.     

A study of the cesium cation bonding to carboxylate anions by the kinetic method and quantum chemical calculations

Collision‐induced dissociation (CID) of the Cs⁺ heterodimer adducts of the nitrate anion (NO₃^?) and a variety of substituted benzoates (XBenz^?) [(XBenz^?)(Cs⁺)(NO₃^?)]^? produces essentially nitrate and benzoate ions. A plot of the natural logarithm of their intensity ratio, ln[I (NO₃^?)/I(XBenz^?)], versus the calculated cesium cation affinity (DFT B3LYP) of the substituted benzoate ions (equivalent to the enthalpy of heterolytic dissociation of the salt) is reasonably linear. This suggests that the kinetic method can be used as a source of data on the intrinsic interaction between the anionic and the cationic moieties in a salt. Copyright © 2010 John Wiley & Sons, Ltd.     

Development of optimized MST/SCRF methods for semiempirical calculations: The MNDO and PM3 Hamiltonians

The self-consistent reaction field (SCRF) method proposed by Miertus, Scrocco, and Tomasi (MST) has been optimized for MNDO and PM3 semiempirical Hamiltonians. Different algorithms used to compute the molecular electrostatic potential (MEP) and different solute cavities have been investigated. The ability of the optimized models to reproduce experimental free energies of solvation and to mimic the solvent effect in several chemical processes has been compared with the ab initio and AM1 versions of the MST method as well as with experimental data. © 1995 by John Wiley & Sons, Inc.     

Thermodynamic stability of the dimerization products of unsubstituted phenoxyl radicals according to data from quantum-chemical calculations determined by the MNDO method

The intermediate dimerization products of PhO^. of the C-O type are more stable than the C-C dimers, while the reverse relationship is. observed for the terminal products. The relative reactivity of the different centers in the phenoxyl radical correlates with the corresponding reorganization energies of the radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2267–2271, October, 1989.     

Investigation of Potential Energy Surface of Thioformaldehyde-S-S-dioxide by MNDO Method

Potential energy surface of thioformaldehyde-S-S-dioxide (sulfene) was of complicated multiextremal character with minima corresponding to several isomers; the structure and interconversion thereof was studied by MNDO method. The structural dynamics of sulfene is the main reason of its abnormally high reactivity.     

Quantum-chemical calculations by the MNDO method of the pre-exponential factor for the homolytic decomposition of aliphatic nitro and α-fluoronitro compounds in the gas phase

The MNDO method has been used to calculate the pre-exponential factor A for the homolytic decomposition of aliphatic nitro and -fluoronitro compounds. It is shown that the high value of A is due to the decrease in the frequencies of the deformation vibrations in the activated complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 339–344, February, 1990.The authors are grateful to K. Ya. Burshtein for his helpful criticism in discussing this work.     

Studies on organophosphorus compounds 52.Structure-reactivity studies of organophosphorus compounds by MNDO calculations

MNDO and MM2(85)methods were used to study the conformation and the structure-reactivity relationship of neutral and acidic phosphorus esters.The calculation results indicate thatfor the most stable conformation,the charge density of phosphoryl oxygen(q_O)is determined notonly by the electronegativity of the substituents,but also by the conformation of the alkoxyl groupson the phosphorus atom.Meanwhile,the conformation of the alkoxyl group provides,as a rule,more important influence on the charge density of the phosphoryl oxygen.However,the energy ofthe highest occupied molecular orbital(EHOMO)is basically dependent on the eletronegativity of thesubstituents,while the donating ability or the withdrawing ability of the neutral phosphorus com-pounds is mainly governed by the EHOMO but not the q_O.This is also true for other kinds of theneutral oxygen-containing compounds.     

The site of radical attack at the furan ring from MNDO calculations

The semi-empirical SCF MNDO method has been used to calculate the radical reactivities for each reaction site in some neutral furan molecules as the average of the HOMO and LUMO probabilities both in 2p_z atomic orbitals 1

1 SCF: Self-consistent field; MNDO: modified neglect of differential overlap; HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital.

. The carbon atoms C⁵ and C² of of the furan ring are the most favoured sites except for the furan derivatives holding a double bond in the substituent group. Also the SOMO 2

2 SOMO: Single occupied molecular orbital.

probabilities of the radicals formed by addition of a hydrogen atom or a vinyl acetate model radical were calculated. Thus, once a radical is added to the C⁵ position the resulting radical can be partially localized on the carbon C². Furthermore, the enthalpy of reaction for several radicals was estimated by using the calculated heats of formation of the neutral furan molecules and their radicals. The radical addition to the carbon C ⁵ resulted in the most exothermic reaction in comparison with other reaction sites of the molecule. However, no correlation was found between the calculated enthalpies and the degradative-transfer kinetic constants experimentally determined for the radical polymerization of vinyl acetate in the presence of the furan compounds under study.     

天冬氨酸热解机理的MNDO研究

本文用MNDO方法全优化计算了天冬氨酸及其热解的中间产物和产物分子的几何构型.通过对计算结果如键长,键级,双原子作用能以及总能量与键长R~C~-~C,R~C~-~N变化关系的分析,提出了天冬氨酸的热解机理,与实验结果基本相符, 但关于中间产物的热解,我们认为很可能是先失去CO~2,而不是CO