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Pham H.T.,Institute for Computational Science and Technology at Ho Chi Minh City ICST | Duong L.V.,Institute for Computational Science and Technology at Ho Chi Minh City ICST | Pham B.Q.,Institute for Computational Science and Technology at Ho Chi Minh City ICST | Nguyen M.T.,Ho Chi Minh City University of Technology
Chemical Physics Letters | Year: 2013

DFT TPSSh/6-311+G(d) calculations are carried out on a series of 2D and 3D forms of Bn, n = 20, 22 and 24 in different charge states. For a certain size, the relative energy within a pair of two-dimensional quasi-planar (2D) and three-dimensional staggered double-ring (3D) boron cluster isomers may shift the sign as they reach a certain charge state. Specifically, electron addition tends to enhance the stability of the 2D over the corresponding 3D isomer irrespective of the available electrons. Linear correlations between 2D-3D relative energy and net charge are established. Along with 2D-to-3D geometry hopping at critical size, our results suggest a local 2D-3D geometry hopping via critical charge. © 2013 Elsevier B.V. All rights reserved.


Cuong N.T.,Hanoi National University of Education | Nguyen H.M.T.,Hanoi National University of Education | Nguyen M.T.,Catholic University of Leuven | Nguyen M.T.,Institute for Computational Science and Technology at Ho Chi Minh City ICST
Physical Chemistry Chemical Physics | Year: 2013

Optical properties of silver Agn nanoclusters are demonstrated to be dependent on their size, structure and charge state. It is found that when being contained in the sodalite cavity of LTA zeolite the tetradecanuclear hexacation silver cluster Ag14 6+ is stable. Its lower-lying states and optical spectrum are theoretically determined using the quantum chemical TD-DFT method. Its ground state possesses an outer-shell electron configuration of A1g 2T2g 6 mimicking the s2p6 valence of noble gas atoms. These frontier orbitals are constructed from 5s,5p(Ag)-AOs with contributions from framework oxygen atoms. Light absorption of Ag14 6+ embedded in the sodalite cage which is characterized by strong peaks centered at 331 and 476 nm (transitions 5s,p(Ag) → 5s,p(Ag)) leads to much longer wavelength emission. The sodalite cage, as a container, stabilizes the central Ag14 6+ cluster by electrostatic attraction. The absorption spectrum of the isovalent neutral Ag8 cluster embedded inside the same sodalite cavity is also simulated using TD-DFT and CASPT2 methods. This absorption spectrum which is similar to that of the Ag14 6+ cluster has two absorption bands in the near UV and visible regions. This journal is © 2013 the Owner Societies.


Huong V.T.T.,Catholic University of Leuven | Nguyen H.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 Ho Chi Minh City ICST
Journal of Physical Chemistry C | Year: 2013

We performed a theoretical investigation on a series of π-conjugated organic molecules containing naphtho[2,3-b]thiophene and their derivatives using density functional theory calculations. All molecules considered exhibit planar structures and aromaticity. Energy levels of frontier orbitals and reduction and oxidation potentials of these compounds predicted by our solvation model reveal good agreement with available experimental values. The UV absorption spectra point out a clear trend that maximum peaks corresponding HOMO-LUMO transitions are red-shifted: (i) from compounds containing O to those containing Se, (ii) from dimers 1a-3a and 1b-3b to trimers 4a-6a and 4b-6b, and (iii) from parent compounds 1a-6a to perfluorinated derivatives 1b-6b. Parent compounds 1a-6a can be considered as p-type semiconducting materials with low reorganization energies, high transfer integrals, and hole mobility. Perfluorinated compounds 1b-6b are suggested to be very good candidates for ambipolar semiconducting materials. Introduction of fused-ring core molecules considerably improves the charge transport characteristics of the co-oligomers 4a-6a and 4b-6b as compared to those of corresponding molecules 1a-3a and 1b-3b. Accordingly, the former have lower reorganization energies, higher electron transfer integrals, and higher rates of charge hopping. © 2013 American Chemical Society.

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