Min Xin-min

Electronic structure and chemical bond of titanium diboride

Titanium diboride was calculated by the density function and discrete variational (DFT-DVM) method to study the relation between structure and properties. Titanium and its first-nearest boron atoms form a strong covalent bond, so TiB2 has high melting point, hardness and chemical stability. Titanium atom releases two electrons to form Ti2+ ions, and a boron atom gets one electron to come into B− ion. B− takes the sp2 hybrid and forms σ bonds to link other boron atoms in the same layer. The other one 2pz orbital of every B− ion in the same layer interacts each other to form the π molecular orbital, so TiB2 has fine electrical property. The calculated density of state is close to the result of XPS experiment of TiB2. Mainly Ti3d and B2p atomic orbitals contribute the total DOS near the Fermi level.

Reaction activity of kaolinite surfaces: Quantum chemistry calculations

The anion-kaolinite surface interactions and AuS− adsorption onto the surfaces of kaolinite were studied using the self-consistent-field discrete variation (SCF-Xα-DV) method. Electronic structure and energies of the system of anion AuS− adsorbed on an atomic cluster of kaolinite were calculated. The results show that the systems with lower total energy are those AuS− adsorbed on the edge surfaces, which indicates that the systems of adsorption of AuS− on the edges are more stable relative to those adsorbed on the basal plane. On the other hand, bond order data suggest that significant shifting of atomic charge and the overlapping of electronic cloud between Au (I) of the AuS− and the surface ions of kaolinite would take place in the systems with AuS− being adsorbed on the edges, especially at the site near Al octahedra. Therefore, it can be concluded that edge sites will dominate the complexation reactions of the surfaces of kaolinite, with negligible contributions from other functional groups on the basal plane, which are dominated by either siloxane sites in silica layers or aluminol sites in gibbsite layers.

Study on the structure and characteristic of dicalcium silicate with quantum chemistry calculations

Abstract The structure and characteristics of β and γ dicalcium silicate (C 2 S), cement clinker minerals, have been studied by the self-consistent-field discrete variational X a method (SCF-DV-X a ), one of the quantum chemistry calculating methods. The results show that there are less differences of SiO bonds between β and γ−C 2 S, the non-regular octahedra of [CaO 6 ] with distortion is more stable than the regular one without distortion, and the main reason why β −C 2 S possess higher hydraulic reactivity than γ−C 2 S lies in the weaker CaO ionic bond in β-C 2 S.

Quantum chemistry calculation on oxygen and nitrogen adsorption in carbon nanotude

Oxygen and nitrogen adsorption in single-walled carbon nanotube (SWCNT) is studied by density function and discrete variational (DFT-DVM) method. The models of O2 and N2 adsorption in the SWCNT are optimized based on the energy minimization. The calculated results of density of state, populations and energy gaps of the molecular orbitals show that oxygen adsorption in SWCNT increases the carbon nanotube’s electrical conductivity more notably than nitrogen adsorption, which is consistent with the experiment.

Electronic structures and bonding properties of Ti2AlC and Ti3AlC2

The relation among electronic structure, chemical bond and property of Ti2AlC, Ti3AlC2 and doping Si into Ti2AlC was studied by density function and the discrete variation (DFT-DVM) method. After adding Si into Ti2AlC, the interaction between Si and Ti is weaker than that between Al and Ti, and the strengths of ionic and covalent bonds decrease both. The ionic and covalent bonds in Ti3AlC2, especially in Ti-Al, are stronger than those in Ti2AlC. Therefore, in synthesis of Ti2AlC, the addition of Si enhances the Ti3AlC2 content instead of Ti2AlC. The density of state (DOS) shows that there is mixed conductor characteristic in Ti2AlC and Ti3AlC2. The DOS of Ti3AlC2 is much like that of Ti2AlC. Ti2SixAl1−xC has more obvious tendency to form a semiconductor than Ti2AlC, which is seen from the obvious difference of partial DOS between Si and Al 3p.

Study on adsorption of submicrometer gold on kaolinite by quantum chemistry calculations

Abstract The electronic structure and energies of Au atoms adsorbed on an atomic cluster of kaolinite were calculated using the self-consistent-field Discrete Variational (DV) method. A hexagonal ring of SiO4 tetrahedra and three AlO2(OH)4 octahedra, comprising 38 atoms, was used to model the kaolinite crystal flake. An Au atom was used to model the submicrometer Au. Calculations were performed with Au atoms adsorbed at different sites. The systems with lower total energy are those with Au adsorbed on the edge surfaces. The adsorption of Au atoms on the edges is more stable than Au atoms adsorbed on the basal plane. Bond order calculations suggest that significant shifting of atomic charge and overlap of electron clouds between Au and the surface atoms of kaolinite takes place in the systems with Au adsorbed on the edges, especially at sites near Al octahedra.

Electronic structure and thermoelectric properties of Ca3Co4O9

The relation among electronic structure., chemical bond and thermoelectric property of Ca3 C04 O9 was studied using density function and discrete variation method (DFTDVM). The gap between the highest valence band (HVB) and the lowest conduction band (LCB) shows a semiconducting property. Ca3 Co4 O9 consists of CoO2 and Ca2 CoO3 two layers. The HVB and LCB near Fermi level are only mainly from O(2) 2p and Co (2) 3d in Ca2CoO3 layer. Therefore, the semiconducting or thermoelectric property of Ca3 Co4 O9 should be mainly from Ca2 CoO3 layer, but it seems to have no direct relation to the CoO2 layer, which is consistent with that binary oxides hardly have a thermoelectric property, but trinary oxide compounds have quite a good thermoelectric property. The covalent and ionic bonds of Ca2 CoO3 layer are both weaker than those of Co02 layer. Ca plays the role of connections between CoO2 and Ca2 CoO3 layers in Ca3 CO4 O9, decrease the ionic and covalent bond strength, and improve the thermoelectric property.

Thermoelectric properties and electronic structure of Ca3Co2O6

The nanosized Ca3Co2O6 powder was synthesized via sol-gel process. The phase composition was characterized by means of X-ray diffraction. Polycrystalline samples of Ca3Co2O6 were prepared by a sintering procedure of nanosized power. The seebeck coefficient and electrical conductivity of the samples were measured from 450K up to 750K. The results show that the Seebeck coefficient increases with the increasing temperature. The electronic structures were calculated using the self-consistent full-potential linearized augmented plane-wave (LAPW) method within the density functional theory. The relationship between thermoelectric property and electronic structures was discussed.

Quantitative XRD analysis of cement clinker by the multiphase Rietveld method

Quantitative phase analysis of Portland cement clinker samples was performed using an adaptation of the Rietveld method. The Rietveld quantitative analysis program, originally in Fortran 77 code, was significantly modified in visual basic code with windows 9 X graph-user interface, which is free from the constraint of direct utilizable memory 640 k, and can be conveniently operated under the windows environment. The Rietveld quantitative method provides numerous advantages over conventional XRD quantitative method, especially in the intensity anomalies and superposition problems. Examples of its use are given with the results from other methods. It is concluded that, at present, the Rietveld method is the most suitable one for quantitative phase analysis of Portland cement clinker.

Electronic structure and thermoelectric properties of Na and Ni-doped Ca3Co2O6

The electronic structures of Ca3Co2O6, Na and Ni doped models were studied by the quantum chemical software of Cambride Serial Total Energy Package (CASTEP) that is based on density function theory (DFT) and pseudo-potential. The electronic conductivity, seebeck coefficient, thermal conductivity and figure of merit (Z) were computed. The energy band structure reveals the form of the impurity levels due to the substitutional impurity in semiconductors. Na-doped model shows the character of p-type semiconductor, but Ni-doped model is n-type semiconductor. The calculation results show that the electric conductivity of the doped model is higher than that of the non-doped model, while the Seebeck coefficient and thermal conductivity of the doped model are lower than those of the non-doped one. Because of the great increase of the electric conductivity, Z of Na-doped model is enhanced and thermoelectric properties are improved. On the other hand, as the large decline of Seebeck coefficient, Z of Ni-doped model is less than that of the non-doped model.