Cluster Quantum Chemical Study of Triaminotoluene Interaction with a Model Clay Surface

This paper presents the results of an ab initio cluster quantum chemical study at the HF/6-31G level for the triaminotoluene (TAT) molecule interaction with a model clay surface, in particular, a kaolinite-type clay mineral. The latter is characterized by a layer structure that contains three different structure units corresponding to alumina, silica, and an intersection of alumina-silica. According to the obtained results, the physical adsorption of TAT took place both on alumina and silica structure units. In going from silica to alumina-silica units, the two-center adsorption of TAT will result in strong adsorption via formation of a TATH⁺ species stabilized by two strong H bonds. Different channels of interactions of TAT with kaolinite-type clay surfaces (i.e., one-, two-, and three-center adsorption of TAT, an aromatic six-member ring opening of TAT) and its destruction via breaking the methyl-aromatic or amino-aromatic ring bonds are also discussed.     

Comparative discussion of NH

A comparative study of NH ₄ ⁺ formation on aluminosilicate surface and in an aqueous solution of hydrochloric acid has been carried out in the framework of the nonempirical method with a STO-3G basis. It is suggested that the compensation mechanisms of energy consumptions to form protonated species in both cases are similar.

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-3 - NH ₄ ⁺ - . - .

     

On some ways of modifying semiempirical quantum chemical methods

The problems of semiempirical quantum chemical calculations of (a) spin densities in paramagnetic organometallics, (b) hydrogen bonds, and (c) bond energies and the structure of transition-metal compounds are discussed. Some modifications of the existing semiempirical quantum chemical method are presented. An extended NDDO approximation has been developed. This scheme includes explicit symmetric orthogonalization of the core Hamiltonian and the use of Hellmann's effective core potential for core-electron interaction. © 1996 John Wiley & Sons, Inc.     

Ab initio study of the structure of isocytosine–cytosine standard Watson–Crick base pairs in the gas phase and in water

Ab initio quantum chemical studies at the HF and MP2 levels with the 6-31G* basis set were performed for H-bonded isocytosine–cytosine standard Watson–Crick base pairs (denoted as iCC1) in the gas phase and in a water solution. Full geometry optimizations at the HF level without any constraints on the planarity of these complexes were carried out. The water solution was modeled by the explicit inclusion of one, two, four, and six water molecules. Six waters create the first full coordination sphere around the iCC1 base pair. All potentially possible hydration positions of the iCC1 base pair with one and two water molecules were considered. The interaction and solvation energies were corrected for the basis-set superposition error by using the full Boys–Bernardi counterpoise correction scheme. It was shown that inclusion of six instead of one, two, or four water molecules has a crucial effect on the geometry of the iCC1 base pair. In the case of six water molecules, the iCC1 moiety becomes strongly nonplanar, while in the case of a smaller number of water molecules, it deviates only slightly from the planar conformation as is adopted in the gas phase. Based on the results of these calculations, the nature of the specific H-bonding interactions, solvation effects, and the interaction energies are discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 37–47, 1998     

Organic probe molecule adsorption on extended Au(111) surface: a theoretical DFT study

Research on Chemical Intermediates - The cluster approach has been applied to mimic the interactions of probe trans-1,2-bis-(4-pyridyl) ethylene on a gold surface with the aim of discriminating the...     

Quantum Chemical Calculations on the Structure and Adsorption Properties of NO and N2O on Ag+ and Cu+ Ion-Exchanged Zeolites

Ab initio cluster quantum chemical calculations at the Hartree–Fock (HF/Lanl2dz) and correlated second-order Moller–Plesset perturbation theory (MP2/Lanl2dz) levels were performed for NO and N₂O interactions with Ag⁺ and Cu⁺ ion-exchanged zeolites. The interaction energies were estimated in a conventional way and also corrected for basis set superposition errors. It was shown that the highly dispersed Ag⁺ counterions establish twofold coordination to the lattice oxygens on the zeolite surface, similar to the case of Cu⁺ ions. However, both NO and N₂O bind relatively strongly to the Cu active sites of Cu⁺ ion-exchanged zeolites than those of the Ag⁺ site of the Ag⁺ ion-exchanged zeolites. Based on the results of these calculations, the two different forms of adsorption for these molecules on the catalyst surface, the nature of their binding and characteristics of the adsorption properties have been discussed. Finally, some comparisons with the results obtained by a variety of density functional theory calculations on target systems have been presented.     

Combined SSF MO LCAO and correlation density functional method applied to adsorption of atomic hydrogen on lithium clusters

An SSF MO LCAO + CDF Method is developed, in which supplementary to a nonempirical SSF MO LCAO calculation the correlation energy of a many electron system is estimated as a functional of the electron density E_C[]. To check the effectiveness of this procedure for calculating the E_C[] functional, E_C is calculated for monohydrides of elements in the second and third columns of the periodic table. The SSF MO LCAO + CDF is applied to a comparative calculation of the adsorption of atomic hydrogen on lithium clusters with different multiplicity and the role of the electron correlation in this process is established.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 385–392, July–August, 1989.