The structure of electronic energy bands, electric charge distribution and the amount of charge transfer of molecular crystals 1-MCI·（TCNQ）<sub>2</sub> （Ⅰ） and 2-MCI· （TCNQ）<sub>2<...The structure of electronic energy bands, electric charge distribution and the amount of charge transfer of molecular crystals 1-MCI·（TCNQ）<sub>2</sub> （Ⅰ） and 2-MCI· （TCNQ）<sub>2</sub> （Ⅱ） have been studied. The results are: （ⅰ） The dominant contributions to the electrical conductivities for crystals Ⅰ and Ⅱ are from TCNQ molecular columns, and the charge carriers are electrons. （ⅱ） The electrical conduction is mainly due to the hopping of charge carriers between the seats of lattice. （ⅲ） The considerable difference of the electrical conductivities between crystals Ⅰ and Ⅱ is due to the differences between （a） the concentrations of charge carriers n<sub>AⅠ</sub><sup>C</sup>= 0.9988-|e|/cell and n<sub>AⅡ</sub><sup>C</sup>=0.0340-|e|/cell; （b） the widths of the energy bands △E<sub>AⅠ</sub><sup>LU</sup>=0.88 eV and △E<sub>AⅡ</sub><sup>L</sup>U=0.040 eV; （c） the first derivative of E with respect to k, （dE/dk）<sub>K<sub>F</sub>AⅠ</sub><sup>LU</sup>=0.27 eV· and （dE/dk）<sub>K<sub>F</sub>AⅡ</sub><sup>L</sup>U=0.0048 eV·; and （d） the difference of energy barriers for the hopping of charge carriers ∈<sub>Ⅱ</sub>-∈Ⅰ=2.5-8.8 kJ/mol.展开更多
Many materials have been used in nanostructured devices;the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Heterojunctions based on ZnO/Cu2O oxides have recently emerged ...Many materials have been used in nanostructured devices;the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Heterojunctions based on ZnO/Cu2O oxides have recently emerged as promising materials for high-efficiency nanostructured devices. In this work, we are interested in the characterization of the surface and interface through nano-scale modeling based on ab initio (Density Functional Theory (DFT), Local Density Approximation (LDA), Generalized Gradient Approximation (GGA-PBE), and Pseudopotential (PP)). This study aims also to build a supercell containing a ZnO/Cu2O heterojunction and study the structural properties and the discontinuity of the valence band (band offset) from a semiconductor to an-other. We investigate crystal terminations of ZnO (0001) and Cu2O (0001). We calculate the energies of the polar surfaces and the work function in the c-axis for both oxides. We built a zinc oxide layer in the wurtzite structure along the [0001] direction, on which we placed a copper oxide layer in the hexagonal structure (CdI2-type). We choose the method of Van de Walle and Martin to calcu-late the energy offset. This approach fits well with the DFT. Our calculations give us a value that corresponds to other experimental and theoretical values.展开更多
The energy bands,electronic structures of CuN3 and AgN3 crystallines were investigated by periodic ab initio method.The charge density projection shows that there are overlaps of isodensities between the terminal nitr...The energy bands,electronic structures of CuN3 and AgN3 crystallines were investigated by periodic ab initio method.The charge density projection shows that there are overlaps of isodensities between the terminal nitrogen and metallic ion,indicating that the metals and the azides are combined by covalent bonds.The crystal lattice energies are-781.05 and-840.83 kJ/mol for CuN3 and AgN3 respectively.These results approach the data obtained by Gray′s approximate method.The frontier crystal orbital mainly consists of the atomic orbital of azide′s terminal nitrogen.The energy gap for AgN3 is smaller than that of CuN3,and the highest occupied crystal orbitals of AgN-3 consist of both the atomic orbitals of the terminal nitrogen in azide and the silver ion,which facilitates the electron to leap from terminal nitrogen in azide to metallic ion directly.Hence silver azide is slightly more sensitive than copper azide.The elastic coefficients C11,C22 and C33 of CuN3 are predicted to be 96.52,96.86 and 154.06 GPa,C11 and C22 of AgN3 are 303.29 and 138.80 GPa.展开更多
基金Project supported by the National Natural Science Foundation of China.
文摘The structure of electronic energy bands, electric charge distribution and the amount of charge transfer of molecular crystals 1-MCI·（TCNQ）<sub>2</sub> （Ⅰ） and 2-MCI· （TCNQ）<sub>2</sub> （Ⅱ） have been studied. The results are: （ⅰ） The dominant contributions to the electrical conductivities for crystals Ⅰ and Ⅱ are from TCNQ molecular columns, and the charge carriers are electrons. （ⅱ） The electrical conduction is mainly due to the hopping of charge carriers between the seats of lattice. （ⅲ） The considerable difference of the electrical conductivities between crystals Ⅰ and Ⅱ is due to the differences between （a） the concentrations of charge carriers n<sub>AⅠ</sub><sup>C</sup>= 0.9988-|e|/cell and n<sub>AⅡ</sub><sup>C</sup>=0.0340-|e|/cell; （b） the widths of the energy bands △E<sub>AⅠ</sub><sup>LU</sup>=0.88 eV and △E<sub>AⅡ</sub><sup>L</sup>U=0.040 eV; （c） the first derivative of E with respect to k, （dE/dk）<sub>K<sub>F</sub>AⅠ</sub><sup>LU</sup>=0.27 eV· and （dE/dk）<sub>K<sub>F</sub>AⅡ</sub><sup>L</sup>U=0.0048 eV·; and （d） the difference of energy barriers for the hopping of charge carriers ∈<sub>Ⅱ</sub>-∈Ⅰ=2.5-8.8 kJ/mol.
文摘Many materials have been used in nanostructured devices;the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Heterojunctions based on ZnO/Cu2O oxides have recently emerged as promising materials for high-efficiency nanostructured devices. In this work, we are interested in the characterization of the surface and interface through nano-scale modeling based on ab initio (Density Functional Theory (DFT), Local Density Approximation (LDA), Generalized Gradient Approximation (GGA-PBE), and Pseudopotential (PP)). This study aims also to build a supercell containing a ZnO/Cu2O heterojunction and study the structural properties and the discontinuity of the valence band (band offset) from a semiconductor to an-other. We investigate crystal terminations of ZnO (0001) and Cu2O (0001). We calculate the energies of the polar surfaces and the work function in the c-axis for both oxides. We built a zinc oxide layer in the wurtzite structure along the [0001] direction, on which we placed a copper oxide layer in the hexagonal structure (CdI2-type). We choose the method of Van de Walle and Martin to calcu-late the energy offset. This approach fits well with the DFT. Our calculations give us a value that corresponds to other experimental and theoretical values.
文摘The energy bands,electronic structures of CuN3 and AgN3 crystallines were investigated by periodic ab initio method.The charge density projection shows that there are overlaps of isodensities between the terminal nitrogen and metallic ion,indicating that the metals and the azides are combined by covalent bonds.The crystal lattice energies are-781.05 and-840.83 kJ/mol for CuN3 and AgN3 respectively.These results approach the data obtained by Gray′s approximate method.The frontier crystal orbital mainly consists of the atomic orbital of azide′s terminal nitrogen.The energy gap for AgN3 is smaller than that of CuN3,and the highest occupied crystal orbitals of AgN-3 consist of both the atomic orbitals of the terminal nitrogen in azide and the silver ion,which facilitates the electron to leap from terminal nitrogen in azide to metallic ion directly.Hence silver azide is slightly more sensitive than copper azide.The elastic coefficients C11,C22 and C33 of CuN3 are predicted to be 96.52,96.86 and 154.06 GPa,C11 and C22 of AgN3 are 303.29 and 138.80 GPa.
