By the particle-swarm optimization method, it is predicted that tetragonal P42mc, 141md, and orthorhombic Amm2 phases of vanadium nitride （VN） are energetically more stable than NaCl-type structure at 0 K. The entha...By the particle-swarm optimization method, it is predicted that tetragonal P42mc, 141md, and orthorhombic Amm2 phases of vanadium nitride （VN） are energetically more stable than NaCl-type structure at 0 K. The enthalpies of the predicted three new VN phases, along with WC, NaC1, AsNi, CsCl type structures, are calculated each as a function of pressure. It is found that VN exhibits the WC-to-CsCl type phase transition at 256 GPa. For the considered seven crystal- lographic VN phases, the structures, elastic constants, bulk moduli, shear moduli, and Debye temperatures are investigated. Our calculated equilibrium structural parameters are in very good agreement with the available experimental results and the previous theoretical results for the NaC1 phase. The Debye temperatures of VN predicted three novel phases, which are all higher than those of the remaining structures. The elastic constants, thermodynamic properties, and elastic anisotropies of VN under pressure are obtained and the mechanical stabilities are analyzed in detail based on the mechanical stability criteria. Moreover, the effect of metallic bonding on the hardness of VN is also investigated, which shows that VNs in P42mc, 141md, and Amm2 phases are potential superhard phases. Further investigation on the experimental level is highly recommended to confirm our calculations presented in this paper.展开更多
The electronic structures of BaMgF4 crystals containing an F colour centre are studied within the framework of the fully relativistic self-consistent Direc-Slater theory, using a numerically discrete variational （DV...The electronic structures of BaMgF4 crystals containing an F colour centre are studied within the framework of the fully relativistic self-consistent Direc-Slater theory, using a numerically discrete variational （DV-Xa） method. It is concluded from the calculated results that the energy levels of the F colour centre are located in the forbidden band. The optical transition energy from the ground state to the excited state for the F colour centre is about 5.12 eV, which corresponds to the 242-nm absorption band. These calculated results can explain the origin of the absorption bands.展开更多
First principles calculations are preformed to systematically investigate the electronic structures, elastic and thermodynamic properties of the monoclinic and orthorhombic phases of Si C2N4 under pressure. The calcul...First principles calculations are preformed to systematically investigate the electronic structures, elastic and thermodynamic properties of the monoclinic and orthorhombic phases of Si C2N4 under pressure. The calculated structural parameters and elastic moduli are in good agreement with the available theoretical values at zero pressure. The elastic constants of the two phases under pressure are calculated by stress–strain method. It is found that both phases satisfy the mechanical stability criteria within 60 GPa. With the increase of pressure, the degree of the anisotropy decreases rapidly in the monoclinic phase, whereas it remains almost constant in the orthorhombic phase. Furthermore, using the hybrid density-functional theory, the monoclinic and orthorhombic phases are found to be wide band-gap semiconductors with band gaps of about 2.85 e V and 3.21 e V, respectively. The elastic moduli, ductile or brittle behaviors, compressional and shear wave velocities as well as Debye temperatures as a function of pressure in both phases are also investigated in detail.展开更多
Using the particle swarm optimization algorithm on crystal structure prediction,we first predict that Mg Y alloy undergoes a first-order phase transition from Cs Cl phase to P4/NMM phase at about 55 GPa with a small v...Using the particle swarm optimization algorithm on crystal structure prediction,we first predict that Mg Y alloy undergoes a first-order phase transition from Cs Cl phase to P4/NMM phase at about 55 GPa with a small volume collapse of 2.63%.The dynamical stability of P4/NMM phase at 55 GPa is evaluated by the phonon spectrum calculation and the electronic structure is discussed.The elastic constants are calculated,after which the bulk moduli,shear moduli,Young's modui,and Debye temperature are derived.The brittleness/ductile behavior,and anisotropy of two phases under pressure are discussed in details.Our results show that external pressure can change the brittle behavior to ductile at10 GPa for Cs Cl phase and improve the ductility of Mg Y alloy.As pressure increases,the elastic anisotropy in shear of Cs Cl phase decreases,while that of P4/NMM phase remains nearly constant.The elastic anisotropic constructions of the directional dependences of reciprocals of bulk modulus and Young's modulus are also calculated and discussed.展开更多
Using first-principles calculations, we investigate the two-dimensional arsenic nanosheet isolated from bulk gray arsenic. Its dynamical stability is confirmed by phonon calculations and molecular dynamics analyzing. ...Using first-principles calculations, we investigate the two-dimensional arsenic nanosheet isolated from bulk gray arsenic. Its dynamical stability is confirmed by phonon calculations and molecular dynamics analyzing. The arsenic sheet is an indirect band gap semiconductor with a band gap of 2.21 e V in the hybrid HSE06 functional calculations. The valence band maximum（VBM） and the conduction band minimum（CBM） are mainly occupied by the 4p orbitals of arsenic atoms,which is consistent with the partial charge densities of VBM and CBM. The charge density of the VBM G point has the character of a π bond, which originates from p orbitals. Furthermore, tensile and compressive strains are applied in the armchair and zigzag directions, related to the tensile deformations of zigzag and armchair nanotubes, respectively. We find that the ultimate strain in zigzag deformation is 0.13, smaller than 0.18 of armchair deformation. The limit compressive stresses of single-layer arsenic along armchair and zigzag directions are-4.83 GPa and-4.76 GPa with corresponding strains of-0.15 and-0.14, respectively.展开更多
The objective of this study was to investigate the hemocompatibility and cell responses to some novel poly（L-lactide） （PLA） composites containing surface modified hydroxyapatite particles for potential application...The objective of this study was to investigate the hemocompatibility and cell responses to some novel poly（L-lactide） （PLA） composites containing surface modified hydroxyapatite particles for potential applications as a bone substitute material. The surface of hydroxyapatite （HA） particles was first grafted with L-lactic acid oligomers to form grafted HA （g-HA） particles. The g-HA particles were further blended with PLA to prepare g-HA/PLA composites. Our previous study has shown signifi- cant improvement in tensile properties of these materials due to the enhanced interracial adhesion between the polymer matrix and HA particles. To further investigate the potential applications of these composites in bone repair and other orthopedic sur- geries, a series of in vitro and in vivo experiments were conducted to examine the cell responses and hemocompatibility of the materials. In vitro experiments showed that the g-HA/PLA composites were well tolerated by the L-929 cells. Hemolysis of the composites was lower than that of pure PLA. Subcutaneous implantation demonstrated that the g-HA/PLA composites were more favorable than the control materials for soft tissue responses. The results suggested that the g-HA/PLA composites are promising and safe materials with potential applications in tissue engineering.展开更多
Symmetry can dramatically reduce the computational cost （running time and memory allocation） of Self-Consistent-Field ab initio calculations for crystalline systems. Crucial for running time is use of symmetry in th...Symmetry can dramatically reduce the computational cost （running time and memory allocation） of Self-Consistent-Field ab initio calculations for crystalline systems. Crucial for running time is use of symmetry in the evaluation of one- and two-electron integrals, diagonalization of the Fock matrix at selected points in reciprocal space, reconstruction of the density matrix. As regards memory allocation, full square matrices （overlap, Fock and density） in the Atomic Orbital （AO） basis are avoided and a direct transformation from the packed AO to the SACO （Symmetry Adapted Crystalline Orbital） basis is per- formed, so that the largest matrix to be handled has the size of the largest sub-block in the latter basis. We here illustrate the effectiveness of this scheme, following recent advancements in the CRYSTAL code, concerning memory allocation and direct basis set transformation. Quantitative examples are given for large unit cell systems, such as zeolites （all-silica faujasite and silicalite MF1） and garnets （pyrope）. It is shown that the full SCF of 3D systems containing up to 576 atoms and 11136 Atomic Orbitals in the cell can be run with a hybrid functional on a single core PC with 500 MB RAM in about 8 h.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11247222,51001042,and 11174102)the Henan Joint Funds of the National Natural Science Foundation of China (Grant No.U1304612)+2 种基金the Natural Science Foundation of Education Department of Henan Province,China (Grant Nos.2011B140015 and 2010B140012)the China Postdoctoral Science Foundation (Grant No.20110491317)the Nanyang Normal University Science Foundation,China (Grant Nos.ZX2012018 and ZX2013019)
文摘By the particle-swarm optimization method, it is predicted that tetragonal P42mc, 141md, and orthorhombic Amm2 phases of vanadium nitride （VN） are energetically more stable than NaCl-type structure at 0 K. The enthalpies of the predicted three new VN phases, along with WC, NaC1, AsNi, CsCl type structures, are calculated each as a function of pressure. It is found that VN exhibits the WC-to-CsCl type phase transition at 256 GPa. For the considered seven crystal- lographic VN phases, the structures, elastic constants, bulk moduli, shear moduli, and Debye temperatures are investigated. Our calculated equilibrium structural parameters are in very good agreement with the available experimental results and the previous theoretical results for the NaC1 phase. The Debye temperatures of VN predicted three novel phases, which are all higher than those of the remaining structures. The elastic constants, thermodynamic properties, and elastic anisotropies of VN under pressure are obtained and the mechanical stabilities are analyzed in detail based on the mechanical stability criteria. Moreover, the effect of metallic bonding on the hardness of VN is also investigated, which shows that VNs in P42mc, 141md, and Amm2 phases are potential superhard phases. Further investigation on the experimental level is highly recommended to confirm our calculations presented in this paper.
基金supported by the Foundation of Shanghai Municipal Education Committee,China (Grant No. 09YZ210)the Shanghai Leading Academic Discipline Project (Grant No. S30502)
文摘The electronic structures of BaMgF4 crystals containing an F colour centre are studied within the framework of the fully relativistic self-consistent Direc-Slater theory, using a numerically discrete variational （DV-Xa） method. It is concluded from the calculated results that the energy levels of the F colour centre are located in the forbidden band. The optical transition energy from the ground state to the excited state for the F colour centre is about 5.12 eV, which corresponds to the 242-nm absorption band. These calculated results can explain the origin of the absorption bands.
基金Projected supported by the Henan Joint Funds of the National Natural Science Foundation of China(Grant Nos.U1304612,U1404608,and U1404216)the Special Fund for the Theoretical Physics of China(Grant No.11247222)+3 种基金the Nanyang Normal University Science Foundation,China(Grant Nos.ZX2010011,ZX2012018,and ZX2014088)the National Natural Science Foundation of China(Grant Nos.11304167 and 51374132)the Postdoctoral Science Foundation of China(Grant No.20110491317)the Young Core Instructor Foundation of Henan Province,China(Grant No.2012GGJS-152)
文摘First principles calculations are preformed to systematically investigate the electronic structures, elastic and thermodynamic properties of the monoclinic and orthorhombic phases of Si C2N4 under pressure. The calculated structural parameters and elastic moduli are in good agreement with the available theoretical values at zero pressure. The elastic constants of the two phases under pressure are calculated by stress–strain method. It is found that both phases satisfy the mechanical stability criteria within 60 GPa. With the increase of pressure, the degree of the anisotropy decreases rapidly in the monoclinic phase, whereas it remains almost constant in the orthorhombic phase. Furthermore, using the hybrid density-functional theory, the monoclinic and orthorhombic phases are found to be wide band-gap semiconductors with band gaps of about 2.85 e V and 3.21 e V, respectively. The elastic moduli, ductile or brittle behaviors, compressional and shear wave velocities as well as Debye temperatures as a function of pressure in both phases are also investigated in detail.
基金Supported by the Henan Joint Funds of the National Natural Science Foundation of China under Grant Nos.U1304612,U1404608the National Natural Science Foundation of China under Grant Nos.51501093,51374132+2 种基金the Special Fund of the Theoretical Physics of China under Grant No.11247222Postdoctoral Science Foundation of China under Grant No.2015M581767Young Core Instructor Foundation of Henan Province under Grant No.2015GGJS-122
文摘Using the particle swarm optimization algorithm on crystal structure prediction,we first predict that Mg Y alloy undergoes a first-order phase transition from Cs Cl phase to P4/NMM phase at about 55 GPa with a small volume collapse of 2.63%.The dynamical stability of P4/NMM phase at 55 GPa is evaluated by the phonon spectrum calculation and the electronic structure is discussed.The elastic constants are calculated,after which the bulk moduli,shear moduli,Young's modui,and Debye temperature are derived.The brittleness/ductile behavior,and anisotropy of two phases under pressure are discussed in details.Our results show that external pressure can change the brittle behavior to ductile at10 GPa for Cs Cl phase and improve the ductility of Mg Y alloy.As pressure increases,the elastic anisotropy in shear of Cs Cl phase decreases,while that of P4/NMM phase remains nearly constant.The elastic anisotropic constructions of the directional dependences of reciprocals of bulk modulus and Young's modulus are also calculated and discussed.
基金supported by the Henan Joint Funds of the National Natural Science Foundation of China(Grant Nos.U1304612 and U1404608)the National Natural Science Foundation of China(Grant Nos.51374132 and 11404175)+1 种基金the Special Fund for Theoretical Physics of China(Grant No.11247222)Nanyang Normal University Science Foundation,China(Grant Nos.ZX2012018 and ZX2013019)
文摘Using first-principles calculations, we investigate the two-dimensional arsenic nanosheet isolated from bulk gray arsenic. Its dynamical stability is confirmed by phonon calculations and molecular dynamics analyzing. The arsenic sheet is an indirect band gap semiconductor with a band gap of 2.21 e V in the hybrid HSE06 functional calculations. The valence band maximum（VBM） and the conduction band minimum（CBM） are mainly occupied by the 4p orbitals of arsenic atoms,which is consistent with the partial charge densities of VBM and CBM. The charge density of the VBM G point has the character of a π bond, which originates from p orbitals. Furthermore, tensile and compressive strains are applied in the armchair and zigzag directions, related to the tensile deformations of zigzag and armchair nanotubes, respectively. We find that the ultimate strain in zigzag deformation is 0.13, smaller than 0.18 of armchair deformation. The limit compressive stresses of single-layer arsenic along armchair and zigzag directions are-4.83 GPa and-4.76 GPa with corresponding strains of-0.15 and-0.14, respectively.
基金supported by the Research Fund for the Doctoral Program of Higher Education(Grant No.20060217012)
文摘The objective of this study was to investigate the hemocompatibility and cell responses to some novel poly（L-lactide） （PLA） composites containing surface modified hydroxyapatite particles for potential applications as a bone substitute material. The surface of hydroxyapatite （HA） particles was first grafted with L-lactic acid oligomers to form grafted HA （g-HA） particles. The g-HA particles were further blended with PLA to prepare g-HA/PLA composites. Our previous study has shown signifi- cant improvement in tensile properties of these materials due to the enhanced interracial adhesion between the polymer matrix and HA particles. To further investigate the potential applications of these composites in bone repair and other orthopedic sur- geries, a series of in vitro and in vivo experiments were conducted to examine the cell responses and hemocompatibility of the materials. In vitro experiments showed that the g-HA/PLA composites were well tolerated by the L-929 cells. Hemolysis of the composites was lower than that of pure PLA. Subcutaneous implantation demonstrated that the g-HA/PLA composites were more favorable than the control materials for soft tissue responses. The results suggested that the g-HA/PLA composites are promising and safe materials with potential applications in tissue engineering.
基金Compagnia di San Paolo for financial support(Progetti di Ricerca di Ateneo-Compagnia di San Paolo-2011-Linea 1A,progetto ORTO11RRT5)Claudio Zicovich-Wilson acknowledges financial support from Mexican CONACyT through project CB-178853
文摘Symmetry can dramatically reduce the computational cost （running time and memory allocation） of Self-Consistent-Field ab initio calculations for crystalline systems. Crucial for running time is use of symmetry in the evaluation of one- and two-electron integrals, diagonalization of the Fock matrix at selected points in reciprocal space, reconstruction of the density matrix. As regards memory allocation, full square matrices （overlap, Fock and density） in the Atomic Orbital （AO） basis are avoided and a direct transformation from the packed AO to the SACO （Symmetry Adapted Crystalline Orbital） basis is per- formed, so that the largest matrix to be handled has the size of the largest sub-block in the latter basis. We here illustrate the effectiveness of this scheme, following recent advancements in the CRYSTAL code, concerning memory allocation and direct basis set transformation. Quantitative examples are given for large unit cell systems, such as zeolites （all-silica faujasite and silicalite MF1） and garnets （pyrope）. It is shown that the full SCF of 3D systems containing up to 576 atoms and 11136 Atomic Orbitals in the cell can be run with a hybrid functional on a single core PC with 500 MB RAM in about 8 h.
