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Nam P.C.,The University of Da nang | Chandra A.K.,North - Eastern Hill University | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology at HoChiMinh City ICST
Chemical Physics Letters | Year: 2013

Integration of the (RO)B3LYP/6-311++G(2df,2p) with the PM6 method into a two-layer ONIOM is found to produce reasonably accurate BDE(O-H)s of phenolic compounds. The chosen ONIOM model contains only two atoms of the breaking bond as the core zone and is able to provide reliable evaluation for BDE(O-H) for phenols and tocopherol. Deviation of calculated values from experiment is ±(1-2) kcal/mol. BDE(O-H) of several curcuminoids and flavanoids extracted from ginger and tea are computed using the proposed model. The BDE(O-H) values of enol curcumin and epigallocatechin gallate are predicted to be 83.3 ± 2.0 and 76.0 ± 2.0 kcal/mol, respectively. © 2012 Elsevier B.V. All rights reserved. Source


Nam P.C.,The University of Da nang | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology at HoChiMinh City ICST
Chemical Physics | Year: 2013

Bond dissociation enthalpies (BDE) of benzeneselenol (ArSe-H) and its para and meta-substituted derivatives are calculated using the (RO)B3LYP/6- 311++G(2df,2p)//(U)B3LYP/6-311G(d,p) procedure. The computed BDE(Se-H) = 308 ± 8 kJ/mol for the parent PhSe-H is significantly smaller than the experimental value of 326.4 ± 16.7 kJ/mol [Kenttamaa and coworkers, J. Phys. Chem. 100 (1996) 6608] but larger than a previous value of 280.3 kJ/mol [Newcomb et al., J. Am. Chem. Soc. 113 (1991) 949]. The substituent effects on BDE's are analyzed in terms of a relationship between BDE(Se-H) and Mulliken atomic spin densities at the Se radical centers of ArSe (π radicals). Good correlations between Hammett's substituent constants with BDE(Se-H) are established. Proton affinity and ionization energy amount to PA(C 6H5SeH) = 814 ± 4 kJ/mol and IE(C6H 5SeH) = 8.0 ± 0.1 eV. IEs of the substituted benzeneselenols are also determined. Calculated results thus suggest that 4-amino-benzeneselenol derivatives emerge as efficient antioxidants. © 2013 Elsevier B.V. All rights reserved. Source


Huong V.T.T.,Catholic University of Leuven | Tai T.B.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology at HoChiMinh City ICST
Physical Chemistry Chemical Physics | Year: 2012

Following the theme of this special issue, two new compounds, the P-flowers C 16(PH) 8 and C 16(PF) 8, are designed by us and subsequently characterized by quantum chemical computations. Their geometries and infrared signatures are analyzed and compared to those of the well-known sulflower C 16S 8. Their electronic structure and aromaticity are examined using the electron localization function (ELF) and also by the total and partial densities of state (DOS). Both C 16(PF) 6 and C 16(PH) 8 molecules exhibit small energy barrier of electron injection (Φ e = 0.33 eV for the gold electrode for the former, and Φ e = 0.1 eV for the calcium electrode for the latter), remarkably low reorganization energy and high rate of electron hopping. Thus, both theoretically designed P-flower molecules are predicted to be excellent candidates for organic n-type semiconductors. This journal is © 2012 the Owner Societies. Source


Tai T.B.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology at HoChiMinh City ICST
Chemical Communications | Year: 2013

The B6Li8 cluster is a symmetrical 3D complex whose high stability can be understood through the Wade rule and aromaticity. A new mechanism of B-Li chemical bonding is proposed. Importantly, B 6Li8 is predicted to be a promising candidate for hydrogen storage material with gravimetric density reaching up to a theoretical limit of 24%. © The Royal Society of Chemistry 2013. Source


Tam N.M.,Catholic University of Leuven | Tam N.M.,Institute for Computational Science and Technology at HoChiMinh City ICST | Tai T.B.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven
Journal of Physical Chemistry C | Year: 2012

A systematic investigation of the boron-doped silicon clusters Si nB with n ranging from 1 to 10 in the neutral, anionic, and cationic states is performed using quantum chemical calculations. Lowest-energy minima of the clusters considered are identified on the basis of the B3LYP, G4, and CCSD(T) energies. Total atomization energies and thermochemical properties such as ionization energy, electron affinity, and dissociation energies are obtained using the high accuracy G4 (B3LYP-MP4-CCSD(T)) and CCSD(T)/CBS (complete basis set up to n = 4) methods. Theoretical heats of formation are close to each other and used to assess the available experimental values. The growth mechanism for boron-doped silicon clusters Si nB with n = 1-10 emerges as follows: (i) each Si nB cluster is formed by adding one excess Si-atom into the smaller sized Si n-1B, rather than by adding B into Si n, (ii) a competition between the exposed (exohedral) and enclosed (endohedral) structures occurs at the size Si 8B where both structures become close in energy, and (iii) the larger size clusters Si 9B and Si 10B exhibit endohedral structures where the B-impurity is located at the center of the corresponding Si n cages. The species Si 9B -, Si 9B, and Si 10B + are identified as enhanced stability systems with larger average binding energies and embedded energies. The higher stability of the closed shells Si 9B - and Si 10B + can be rationalized in terms of the jellium electron shell model and spherical aromaticity. © 2012 American Chemical Society. Source

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