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Femme scientifique et inconscient : les mathématiques
No full textNguyen Minh. Femme scientifique et inconscient : les mathématiques. In: Revue d'en face, n°13, 1983. Les femmes et la science. pp. 19-22
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神経意味解析における言語的特徴と事前訓練された言語モデルの注入
No full textSupervisor: Nguyen Minh Le先端科学技術研究科博士identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/1812
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Computationele studie van silicium clusters gedopeerd door enkele hoofdgroep elementen
No full textThis doctoral thesis reports the theoreticalinvestigations on the geometrical and electronic structures of small siliconclusters doped with some representative main group elements, including Li, Mg,B, Al and also C by using quantum chemical calculations. Deep understanding oftheir geometric and electronic structures, energetics and bonding phenomenaconstitutes a necessary step in the extensive and intensive search forpromising clusters that could be considered as building blocks for furtherassemblies. Our searches for minima on thepotential energy surfaces were performed using two different approaches. In thefirst, we used a stochastic genetic algorithm to generate as many guessstructures as possible. Equilibrium structures that were initially detectedusing low-level computations, were then reoptimized using higher level methods.In the second approach, we made use of a chemical intuition, in that initialstructures of clusters SinXm were manually constructedby either substituting Si-atoms of the corresponding silicon frameworksby other element atoms, or adding dopant-atoms at various positions on surfacesof the Sin clusters. Theuse of the genetic algorithm is less effective for producing singlydoped-clusters having small sizes because most of relevant structures in Si clustersare relatively well known. On the contrary, the multi-doped and larger sizeclusters imply a huge number of initial guess structures and thus make thegenetic search necessary and more effective, even though such a search is oftentedious and computationally demanding. Nevertheless, only a combination ofdifferent search approaches allows a consistent set of lower-energy structuresto be obtained. We are confident that the isomers reported in this thesis atleast correspond to the lower-energy equilibrium structures. However, not onlya careful search is required, but the accuracy of the computational methodsused is equally crucial in the determination of global minima. The low-lying isomers of the clusterswere identified on the basis of theoretical results obtained by hybrid (U)B3LYPfunctional in conjunction with the 6-311+G(d) basis set (d polarization plus spdiffuse functions), and then the ground states are assigned by high accuracy computationalmethods such as the composite G3B3 and G4 methods and when possible also the coupled-clustertheory extrapolated to the complete basis set CCSD(T)/CBS protocol. Concerningthe energetics, different basic thermochemical parameters of the clustersconsidered including total atomization energies (TAE), standard enthalpies offormation (ΔHf),ionization energies (IE), electron affinities (EA), binding energies (Eb), embedded energy (EE) anddissociation energies (De)were determined using the Gn (G3B3and G4) and CCSD(T)/CBS approaches. For bare silicon clusters, a uniform set of standard heats offormation for the cationic and anionic Sinclusters were determinedfor up to n = 13. Insome cases, variations between G4 and CBS TAE values are relatively large. The differences of energeticproperties between both G4 and CBS methods can be understood from the ways ofcomputing single point electronic energies, as well as the geometries ofclusters used. Geometry is beyond any doubt an important factor in thethermochemical evaluation. For these systems, experimentalresults in the current literature were also characterized by large uncertainties,including the actual uncertainty of the standard heat of formation of the Siatom. For otherparameters such as IEs and EAs,they were better predicted, in part due to a certain mutual cancellation oferrors in the evaluation of relative energies. The corresponding G4 results areexpected to be accurate to, or even better than, ± 0.15 eV. For lithiumdoped silicon clusters, the adiabatic (AIEs) and vertical (VIEs) ionizationenergies of the SinLim clusters were evaluated. CalculatedAIE and VIE values at the B3LYP/6/311+G(d) and CCSD(T)/aug-cc-pVDZ levels forSi6Li2, Si7Li, Si10Li, Si11Licompare quite well with the corresponding experimental results obtained usingthe photo-ionization efficiency measurements.For borondoped silicon clusters, heats of formation calculated by both G4 andCCSD(T)/CBS methods showed good agreement with available experimental data.Overall, it appears that an accurateevaluation of the TAEs and thereby the standard heats of formation of silicon-basedclusters remains a great challenge for quantum chemical computations in order to attain thechemical accuracy of ± 1.0 kcal/mol. Due to the non-classical bonding of clusters,the use of other thermochemical approaches (such as bond separation reactions)and more economic computational methods could not be applied. The only optionleft is to increase the quality of the wavefunctions in going beyond theCCSD(T) level. However, our preliminary computations using the full CCSDT treatmentpointed out that it is much more computer-demanding than the CCSD(T) method,which goes beyond our actual computing resources. Based on the geometricalcharacteristics of the ground states, a growth mechanism for each series ofbinary silicon clusters SinXm can now beestablished. Generally, alkali (Li) orearth-alkali (Mg) dopants prefers add on an edge or a face of Sin frameworks, whereas theboron group 13 element (B, Al) favors substitution into one of the Si positionsin Sin+1counterparts. Due to the shorter B-Si bond lengths, as compared with the Al-Si counterparts,the B impurity can intrude inside the corresponding Sin cage (for up to n≥ 8). In particular, the neutral structures of doubly impurities doped siliconclusters SinX2,(X = Li, Mg, Al) have similar way of growing up: one dopant atom substitutesinto a position of Sin+1,whereas the other is usually added on an edge, or a face, of the existingcluster.Our theoretical results also predicted that some closed-shellsystems such as Si9B-, Si10B+ , Si9Al-,and Si4C2+ are characterized by enhanced stabilities. Theirhigher thermodynamic stabilities can be understood by the Jellium shell model(JSM). According to JSM, the valence electrons are supposed to befreely itinerant in a simple mean-field potential formed by the nuclei of atomsand core electrons, the valence electrons fill the hydrogen-like orbitals ‌‌followingthe pattern of orbitals as [1S21P61D102S21F142P61G182D10
]etc
Within this model, the numbers of valence electrons of 8, 20, 34, 40, 56and 68
emerge as the magic numbersthat actually correspond to a complete filling of the successive shellelectrons. Concerning the bonding phenomena, electron localization techniques (ELF and ELI-D)were used to locate the whereabouts of electrons, and thereby toidentify the chemical bonds of some specific clusters such as Si3,Si4, Si42+, Si4C2+, andSi9C. Calculations of the ring current, which is the magneticresponse of a molecule, were also carried out in order to probe their aromaticity. This study provided a further supportfor the point of view that the existence of delocalized occupied molecularorbitals in a planar molecule is a necessary but not sufficient condition toassign a certain aromatic character (aromatic, non-aromatic or anti-aromatic)to that specific type of electrons. Different criteria (such as the magneticring current) need to be considered for a more consistent evaluation of thispopular but intriguing molecular property. In addition, both the Si4C2+dication and the SiC9 neutral exhibit a planar tetracoordinatecarbon atom (ptC) in their lowest-lying isomer. This is caused by a drivingforce for C-planarization which includes not only the electron delocalizationon the square frame but also the bonding between C-dopant and the Si frame of thesmall dication. In the larger neutral cluster cage, the Si5 grouptends to stabilize electronically the cage by electron transfer but alsomechanically by geometrical constraints in maintaining a ptC configuration. We also attempted to search for potential linkers in makingsilicon nanowires. We found that the Mg dopant, due to its large electrontransfer capacity, behaves as a cation Mgdelta+ and thereby induces anionic entity with the Sindelta-anionic partner. The resulting Mg cation can be served as a linker between Sin blocks leading tostabilized linear [(Sik)Mg]lstructures in part due to electrostatic attraction forces. This allowed us to identify some suitable membersthat can further be used as superatoms for assemblies. We thus probed thefive-, seven-, eight- and ten-atom Si building blocks, and the role of the Mgelement as the linkers connecting them. Calculated results ofthe average assembling energy which gave us an idea about the tendency ofassembling the cluster of (SikMg)l with k = 5, 7, 8, 10, show that silicon clusters Sik tend to assemble in ring forms (Rl) over the linear forms(Ll)as the assembling energy of the Rl are larger than those of the Ll.However, a more important fact is that the average assembling energy of thelinear form tends to increase with the increasing size (l), implying that a(longer) nanowire can be considered as a plausible possibility.status: Publishe
Studies on antibacterial and cytotoxic secondary metabolites of Vietnamese marine sponges Spongia sp.,Xestospongia testudinaria and Clathria reinwardti
Get PDF富山大学博士（薬科学）Article富山大学・富医薬博甲第304号・NGUYEN MINH HIEN・2019/03/26・★論文非公開
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