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Transition State Theory, with Wigner tunneling correction, was employed to determine the thermal rate coefficients for the first excited state of the H+ + LiH reaction using the potential energy surface calculated and fitted by Martinazzo et al. [Martinazzo et al., J Chem Phys 2003, 119, 11241]. The calculated thermal rate coefficients, in the temperature range of 500–1,000 K, are near to the value of 10-9 cm3 s-1 and tend to a constant value (10-8 cm3 s-1) at lower temperatures (200 K). These results support the recent investigation of Bulut et al. that showed the TRC to be nearly independent of temperature. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

The H-bonded complexes formed from interaction between NH2NO (NA) and H2O2 (HP) have been investigated by using B3LYP and MP2 methods with a wide range of basis sets. We found six H-bonded complexes in which three of them have cyclic structure. Calculations carried out at various levels show that the seven-membered cyclic structure with O···HO and O···HN hydrogen bonding interactions is the most stable complex. The large binding energy obtained for A1 complex probably results from a more linear arrangement of the O···H&bond;N and O&bond;H···OH-bonds in the seven-membered structure A1. The natural bond orbital (NBO) analysis and the Bader's quantum theory of atoms in molecules have been used to elucidate the interaction characteristics of the NA-HP complexes. The NBO results reveal that the charge transfer energy corresponds to the H-bond interactions for A1 complex is grater than other complexes. The electrostatic nature of H-bond interactions is predicted from QTAIM analysis. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

We have studied H2 adsorption on C3H3V organometallic compound using density functional method at B3LYP/LanL2Dz level of theory. It was found that H2 molecule dissociates and adsorbed in dihydride form on this organometallic compound. Potential energy surface for H2 dissociation process was obtained and different properties such as HOMO–LUMO gap, dipole moment, interaction energies between different molecules and atoms, vibrational frequencies, and atomic charges during the dissociation process were studied. It was found that the C3H3V(H2) structure is most stable at H&bond;V&bond;H angle of 66.3°. Many-body analysis was also carried out to determine the two-body energies, three-body energies, relaxation energy, and binding energy of the structures for each point on the potential surface. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

This study is intended as a continuation of previous experimental and theoretical works on the systems H2O-Rg, H2S-Rg, H2O2-Rg, and H2S2-Rg, where Rg = He, Ne, Ar, Kr, Xe. For the H2O-Rg and H2S-Rg systems, molecular and atomic polarizabilities have been calculated and from them, using phenomenological correlation formulas modeling the dispersion-repulsion (van der Waals) forces, the isotropic interaction parameters have been determined and compared with experimental data from this laboratory. For the H2O2-Rg and H2S2-Rg systems, the molecular polarizabilities have been calculated and used in correlation formulas to predict well depths and positions of van der Waals forces and a comparison made with the corresponding potential energy surfaces calculated in previous works. The approach correctly predicts the interaction parameters, except for H2O and H2O2 with the heavier rare gases. The correlation formulas have been then extended to include an attractive induction contribution accounting for the interaction between the permanent molecular dipole moment and the instantaneous induced atomic dipole moment, to improve the predicted parameters for H2O and H2O2-Ar, Kr and Xe. The agreement with experimental and theoretical data is improved but the predicted data still underestimate the interaction. This is probably due to the presence of a significant non van der Waals contribution to the interaction for the heavier gases, as suggested by analogy with the previously studied water-Rg case. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

In this article we present a characterization of the vibrational spectrum of the H5+ molecule using the correlation function quantum Monte Carlo (CFQMC) method and a genetic algorithm study of the topology of the potential energy surface (PES) used. The vibrational modes associated with the H3+-H2 torsion and stretching possess very flat minima. As a consequence the fundamental frequencies corresponding to these modes are poorly described in the harmonic approximation. In our genetic algorithm study of the PES using Cartesian coordinates we have found some unexpected minima. A careful analysis shows that, in the curvilinear coordinates in which the potential is described, some of these minima have identical coordinates. Nevertheless, they represent nonequivalent molecular geometries. The vibrational frequencies obtained in this work are not in good agreement with available experimental data as well as other computational methods. It shows that our method of detailed analysis of PESs could reveal shortcomings introduced by the use of curvilinear coordinates. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

The q-Integral method, based on the q-Exponential function, has been recently introduced as an alternative approach to calculate the two-electron integrals which appear in ab initio atomic and molecular quantum mechanical calculations. The advantage of this procedure is that the CPU time for calculating of two-electron integrals is substantially reduced when compared with the usual one. The objective of this work is to investigate the accuracy of the q-Integrals as a function of the internuclear distance for molecular systems. To this purpose we employed the q-Integrals to construct the potential energy surface (PES) for the H2 molecule and used the PES to determine the rovibrational levels and spectroscopic constants of the molecule, which are properties very sensitive to the form of the PES. The results obtained are in good agreement with the ones obtained through the standard procedure of calculating the two-electron integrals, implying that the q-Integral method is accurate enough to be used in any molecular quantum mechanical calculation. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

Comparison of Hartree–Fock (HF) and Heitler–London (HL) ground-state computations for H2, LiH, Li2, BH, HF, and F2 leads to an approach that is a variational combination of the two approximations. This new HF–HL ab initio method is implemented at three levels. The first level variationally optimizes the linear combination of traditional HF and HL functions. It correctly predicts both molecular formation and dissociation for the above molecules, features not consistently found in either the HF or the HL approximations. The second level introduces valence correlation and the third level inner shells correlation, adapting standard multi-configuration techniques to the HF–HL function. The procedure for both levels has been preliminarily applied to LiH and Li2 and found to yield very encouraging results when compared to experimental data. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

In this article we present the results of a quantum study performed on different models of the active site of methylamine dehydrogenase (MADH). This enzyme catalyzes the oxidation of methylamine to produce formaldehyde and ammonia. During the rate-determinant step of the reaction, a proton is transferred from the methyl group of the substrate to one of the bases of the active site. We performed calculations on three different models of the active site. The number of atoms of the models ranges from 68 to 95. Minimizations and optimizations were performed at the PM3 level of theory. The energies of the optimized structures were then recalculated at the B3LYP 6-31G(d) level. From these energies, we calculated the barriers for H+ transfer toward the putative acceptors of the proton Asp76 and Thr122. By comparing the results of different models against each other, we drew some conclusions about the role of different residues. We found that the H+ transfer from the substrate toward Thr122 requires that this residue be ionized. The estimated barrier for this ionization was found to be >19 kcal/mol. The barrier for H+ transfer from the substrate toward Asp76 is significantly smaller. Our best estimates indicate that this barrier is 9.7 kcal/mol, when the imino group of the substrate is unprotonated and 7.7 kcal/mol when it is protonated. We thoroughly discussed the agreement and disagreement of these values with the results reported in previous theoretical and experimental studies. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

A comparative study of adsorption of H atoms and H2 molecules on Pd3Cu, Cu4, and Pd4 clusters has been performed through density functional calculations, using the hybrid B3LYP exchange‐correlation functional as implemented in the Gaussian98 program. For Pd atoms the relativistic small‐core effective core potential LANL and LANL2DZ basis set was used and for hydrogen a 6‐31G** basis set was used. The main emphasis is set in the reaction behavior of the different clusters with hydrogen atoms and molecules. We find that full geometry optimization does not appreciably change the metal cluster geometry either for certain reaction modes or the H and H2 capture parameters, but increases the number of reactive sites of the metal clusters. Also, we found that there is charge transfer competition between H and Cu atoms, which drastically diminishes H2 adsorption energy, related to the Pd cluster observed value. Edges and threefold sites are the principal hydrogen adsorption sites. Hydrogen has a great mobility over the metal clusters for different minima, especially when Cu is present; many initial pathways end in the same adsorption site. The observed hydrogen adsorption and binding energies are well reproduced by the calculations. Also, the adsorption mechanisms were determined. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]