Institute for Computational Science and Technology of HoChiMinh City

Thu Duc, Vietnam

Institute for Computational Science and Technology of HoChiMinh City

Thu Duc, Vietnam
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Tai T.B.,Catholic University of Leuven | Nhat P.V.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Physical Chemistry Chemical Physics | Year: 2010

Quantum chemical calculations are performed on the aluminium doped lithium clusters LinAl at both neutral and cationic states using the DFT/B3LYP and CCSD(T) methods in conjugation with the aug-cc-pVaZ (a = D,T,Q) basis sets. The global minima are located and the growth mechanism is established. The electronic structure, geometrical parameters and energetic properties, such as average binding energy Eb, second difference of energy Δ2E, adiabatic and vertical ionization energy, and dissociated enthalpy, are evaluated using the coupled-cluster CCSD(T) method, whose energies are extrapolated to the complete basis set limit (CBS). The high stability of Li5Al, Li7Al, Li6Al+ and Li8Al+ that have the "magic numbers" of valence electrons, can be understood using the phenomenological shell model. © 2010 the Owner Societies.


Pham-Tran N.-N.,Ho Chi Minh City University of Technology | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Comptes Rendus Chimie | Year: 2010

A series of oligothiophenes and novel oligophospholes, consisting of fluorinated and perfluoroarene-substituted structures, were investigated using density functional theory (DFT) methods. The study focused on the geometrical structures and electronic properties. The degree of π-conjugation in the neutral oligomers was probed by different approaches including analysis of predicted Raman spectra. The character of the charge carrier of the new substituted oligomers, either electron (n-type doping) or hole (p-type doping) transport, was predicted by comparing their properties, including the frontier orbital HOMO and LUMO, excitation, and reorganization energies, with those of their non-substituted parent oligomers. The quantum chemical DFT results are consistent with available experimental data on the oligothiophenes for both geometries and conductivity properties. The results strongly suggest that an effective way of designing new materials with n-type conductivity is to introduce electron-withdrawing groups into the oligomer backbone. Calculated results were subsequently obtained for oligomers based on 1H-phospholes, which are predicted to have potentially useful properties as novel semiconductor materials. © 2010 Académie des sciences.


Tai T.B.,Catholic University of Leuven | Tam N.M.,Catholic University of Leuven | Tam N.M.,Institute for Computational Science and Technology of HoChiMinh City | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Chemical Physics | Year: 2011

Small zinc-doped tin clusters Sn nZn, n = 1-12, are studied using DFT and CCSD(T) methods. The isomers are located using a stochastic search algorithm. The growth mechanism can be formulated as follows: (i) small clusters Sn nZn with n ≤ 8 are formed by capping Zn on a surface of Sn n, (ii) a competition between exohedral and endohedral structures appears at n = 9 and 10, from which the endohedral structures become predominant, (iii) for n = 11 and 12, the clusters are formed by encapsulating Zn into the empty cages Sn n. Icosahedral Sn 12Zn (I h) and Sn 10Zn (D 4d) are magic clusters with large HOMO-LUMO gaps, high binding energies and embedding energies. While both Sn 12Zn and Sn 10Zn clusters can be considered to be spherically aromatic with 8 valence π-electrons that satisfy the electron count rule of 2(N + 1) 2, the enhanced stability of Sn 12Zn (I h) can further be rationalized in terms of its closed crystal field splitting shell. © 2011 Elsevier B.V. All rights reserved.


Tai T.B.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Chemical Physics | Year: 2010

The electronic structure and molecular properties of a series of small mixed lithium boron clusters BnLi (n = 1-8) in both neutral and anionic states are investigated using quantum chemical methods. The lowest-energy structures are identified. Standard heats of formation, adiabatic electron affinities (EAs) and vertical detachment energies (VDEs) are predicted using coupled-cluster theory CCSD(T)/6-311+G(d) calculations. Addition of Li to Bn to form BnLi clusters marginally distorts the geometries of the parent Bn. The chemical bond in BnLi has a highly ionic character in which the positive charges are located on Li. MO analysis confirms a similar degree of aromaticity between BnLi and Bn-. The relative stabilities of the clusters are evaluated using the average binding energy (Eb), second order difference in energy (Δ2E), resonance energy (RE) and normalized resonance energy (NRE). Both REs and NREs quantities of the Li-doped boron clusters are consistently larger than those of the pure Bn clusters. The B 3Li species exhibits a remarkably high stability within the B nLi series. © 2010 Elsevier B.V. All rights reserved.


Tai T.B.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Chemical Physics Letters | Year: 2010

Structure and stability of the Ge12Mx clusters with M = Li, Na, Be, Mg, B, Al, and x from-1 to +1, each containing 50 valence electrons are investigated using DFT calculations. The global minima turn to be the high symmetry icosahedral structures, with large HOMO-LUMO gaps and high detachment or ionization energies. In particular, Li is found for the first time to be located at the center of an icosahedron Ge12Li-. The high thermodynamic stability of the icosahedra arises from a combination of their closed crystal field shells, spherical aromaticity and electrostatic attraction force. © 2010 Elsevier B.V. All rights reserved.


Tai T.B.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Chemical Physics Letters | Year: 2010

A quantum chemical investigation of the clusters Li5B, Li6B+, Li6B- and Li7B was performed using the DFT, MP2 and CCSD(T) methods. The high symmetry structures (C4v, 1A1), (Oh, 1A1g) and (D5h, 1 A1 ′) turnout to be the global minima for Li5B, Li6B+ and Li7B, respectively. These clusters are predicted to be highly stable species with large vertical ionization energies, and large HOMO-LUMO gaps. Chemical bonding of clusters was probed using an electron localizability indicator (ELI) which indicates a large aromatic character. The high stability of these clusters can be accounted for by the phenomenological shell model. © 2010 Elsevier B.V. All rights reserved.


Lin L.,Catholic University of Leuven | Lievens P.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Chemical Physics Letters | Year: 2010

CO adsorption on AunY (n = 1-9) is investigated using density functional theory, and compared with pure gold clusters Aun +1. CO is confirmed to prefer on-top binding to the least coordinated Au atom for the pure gold clusters, whereas for Y-doped gold clusters, the most favorable sites are dependent on the cluster size; the Au on-top sites are favored from n = 6. CO behaves as an electron acceptor, and the C-O vibrational frequency of the metal-CO complexes correlates with the degree of charge transfer to CO. Reactivity with CO is decreased after one gold atom is replaced by one yttrium for most sizes. © 2010 Elsevier B.V. All rights reserved.


Lin L.,Catholic University of Leuven | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology of HoChiMinh City
Chemical Physics Letters | Year: 2010

CO oxidation on Au2n- (n = 1 - 4) cluster anions are investigated using DFT methods. O 2 prefers to bind on-top to a gold atom. Binding energies of O 2 on Au2n- are in the range of 0.8-1.2 eV. CO molecule can then insert into the O-O bond of Au2nO2- to form carbonate species, that are the most stable Au2nCO3- isomers, and thus expected to play an important role in CO oxidation. The negative charges of the gold carbonates are mainly distributed on the CO 3 moieties. The gold carbonate anions can yield CO 2 by direct dissociation or react with another CO to produce 2(CO 2). © 2010 Elsevier B.V. All rights reserved.


Tai T.B.,Catholic University of Leuven | Kadlubanski P.,Wroclaw University of Technology | Roszak S.,Wroclaw University of Technology | Majumdar D.,Jackson State University | And 3 more authors.
ChemPhysChem | Year: 2011

We perform a systematic investigation on small silicon-doped boron clusters B nSi (n=1-7) in both neutral and anionic states using density functional (DFT) and coupled-cluster (CCSD(T)) theories. The global minima of these B nSi 0/- clusters are characterized together with their growth mechanisms. The planar structures are dominant for small B nSi clusters with n≤5. The B-Si molecule represents a geometrical transition with a quasi-planar geometry, and the first 3D global minimum is found for the B-Si cluster. The small neutral B-Si clusters can be formed by substituting the single boron atom of B- by silicon. The Si atom prefers the external position of the skeleton and tends to form bonds with its two neighboring B atoms. The larger B-Si cluster is constructed by doping Si-atoms on the symmetry axis of the B- host, which leads to the bonding of the silicon to the ring boron atoms through a number of hyper-coordination. Calculations of the thermochemical properties of B clusters, such as binding energies (BE), heats of formation at 0 K (I 0) and 298 K (ΔH f [298]), adiabatic (ADE) and vertical (VDE) detachment energies, and dissociation energies (D e), are performed using the high accuracy G4 and complete basis-set extrapolation (CCSD(T)/CBS) approaches. The differences of heats of formation (at 0 K) between the G4 and CBS approaches for the B nSi clusters vary in the range of 0.0-4.6 kcal mol -1. The largest difference between two approaches for ADE values is 0.15 eV. Our theoretical predictions also indicate that the species B 2Si, B 4Si, B 3Si - and B 7Si - are systems with enhanced stability, exhibiting each a double (σ and π) aromaticity. B 5Si - and B 6Si are doubly antiaromatic (σ and π) with lower stability. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Nhat P.V.,Catholic University of Leuven | Nhat P.V.,Can Tho University | Ngan V.T.,Catholic University of Leuven | Tai T.B.,Catholic University of Leuven | And 2 more authors.
Journal of Physical Chemistry A | Year: 2011

Geometric and electronic structures, vibrational properties, and relative stabilities of niobium clusters Nb n, n = 7-12, are studied using both DFT (BPW91 and M06 functionals) and CCSD(T) calculations with the cc-pVnZ-PP basis set. In each cluster, various lower-lying states are very close in energy in such a way that the ground state cannot be unambiguously established by DFT computations. Nb clusters tend to prefer the lowest possible spin state as the ground state, except for Nb 12 ( 3A g). The optimal structure of the cluster at a certain size does not simply grow from that of the smaller one by adding an atom randomly. Instead, the Nb clusters prefer a close-packed growth behavior. Nb 10 has a spherically aromatic character, high chemical hardness and large HOMO-LUMO gap. Electron affinities, ionization energies, binding energy per atom, and the stepwise dissociation energies are evaluated. Energetic properties exhibit odd-even oscillations. Comparison with experimental values shows that both BPW91 and M06 functionals are reliable in predicting the EA and IE values, but the BPW91 is deficient in predicting the binding and dissociation energies. We re-examine in particular the experimental far IR spectra previously recorded using the IR-MPD and free electron laser spectrometric techniques and propose novel assignments for Nb 7 and Nb 9 systems. The IR spectra of the anions are also predicted. © 2011 American Chemical Society.

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