Zhiming Liu

Publications (5)5.61 Total impact

• Article: Theoretical calculations of phase transitions and optical properties of solid iodine under high pressures

  Xiaojiao San, Liancheng Wang, Yanming Ma, Zhiming Liu, Tian Cui, Bingbing Liu, Guangtian Zou
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  ABSTRACT: The structural stability and optical properties of solid iodine under pressure have been studied using the ab initio pseudopotential plane-wave method. The dependence of lattice parameters on pressure indicates that the first structural phase transition from phase I to phase V occurs at about 20 GPa. From the pressure dependence of our elastic constants for solid iodine in phase I, it is found that the first structural transformation from molecular phase I to the intermediate phase V occurs at about 20 GPa due to the softening of the elastic constant C44, which is very close to the transition pressure of 20 GPa obtained by geometry optimizations and 23.2 GPa obtained by experimental measurements. The optimized structure for phase V is a face-centered orthorhombic (fco) phase with equal interatomic distances d1 = d2 = d3, but this fco structure is mechanically unstable, with shear elastic stiffness coefficient C44<0. To understand the modulated phase V, we use a periodic crystal structure to mimic the incommensurate phase V and obtain some quantitative information. In our calculation, the modulated phase is thermodynamically and mechanically stable. It is believed that phase V is not a monatomic phase but an intermediate state between a molecular and a monatomic state.
  Journal of Physics Condensed Matter 04/2008; 20(17):175225. · 2.55 Impact Factor
• Source

  Available from: arxiv.org

  Article: Ab initio investigation of optical properties of high-pressure phases of ice

  Renjun Xu, Zhiming Liu, Yanming Ma, Tian Cui, Bingbing Liu, Guangtian Zou
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  ABSTRACT: We report a detailed ab initio investigation on the optical properties of ice under a wide high pressure range. The ice X phase (up to 380GPa), the theoretical proposed higher pressure phase ice XV (300GPa), as well as the ambient pressure low-temperature phase ice XI are involved. Our results show that the dispersion relations of optical properties of ice under high pressure are quite different from those under ambient pressure. Under higher pressure, there is whole tendency of blue shift in all optical properties of ice, and the energy region for optical response become broader, such as the absorption band and reflection band. In addition to the augmented absorption edge, all absorption peaks are found to be rising, and the reflection peaks are also enhanced a bit; hence the transmissivity of ice is inferred to be dropping. The photoconductivity is enhanced, and we explain this behavior from the increase of earner density. The static optical properties are found to be pressure independent, and principally due to the network topology of hydrogen bonding.
  01/2008;
• Source

  Available from: arxiv.org

  Article: Ab initio investigation of hydrogen bonding and electronic structure of high-pressure phases of ice

  Renjun Xu, Zhiming Liu, Yanming Ma, Tian Cui, Bingbing Liu, Guangtian Zou
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  ABSTRACT: We report a detailed ab initio investigation on hydrogen bonding, geometry, electronic structure, and lattice dynamics of ice under a large high pressure range, including the ice X phase (55-380GPa), the previous theoretically proposed higher-pressure phase ice XIIIM (Refs. 1-2) (380GPa), ice XV (a new structure we derived from ice XIIIM) (300-380GPa), as well as the ambient pressure low-temperature phase ice XI. Different from many other materials, the band gap of ice X is found to be increasing linearly with pressure from 55GPa up to 290GPa, the electronic density of states (DOS) shows that the valence bands have a tendency of red shift (move to lower energies) referring to the Fermi energy while the conduction bands have a blue shift (move to higher energies). This behavior is interpreted as the high pressure induced change of s-p charge transfers between hydrogen and oxygen. It is found that ice X exists in the pressure range from 75GPa to about 290GPa. Beyond 300GPa, a new hydrogen-bonding structure with 50% hydrogen atoms in symmetric positions in O-H-O bonds and the other half being asymmetric, ice XV, is identified. The physical mechanism for this broken symmetry in hydrogen bonding is revealed.
  01/2008;
• Article: Influence of impurity hydrogen on the structure and properties of bulk Li and pressure effects

  Zhiming Liu, Yanming Ma, Zhi He, Tian Cui, Wenjiong He, Bingbing Liu, Guangtian Zou
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  ABSTRACT: The structure and properties of a 16-atom body-centered cubic lithium cell with an interstitial hydrogen atom are studied using a pseudopotential-plane-wave method within the density functional theory at 0 K and high pressures. The host lattice is dramatically distorted by the introduction of H. Although the hydrogen atom is stable at the tetragonal site in perfect bcc host lattice, it favors the octahedral site formed by six non-equivalent Li atoms after full relaxation of the cell, showing P4/mmm symmetry within the pressures ranging from 0 to 6 GPa. The lattice ratio (a/c) changes irregularly with external pressure at about 3 GPa. The hydrogen band lies in the bottom of the valence band, separated by a gap from the metallic bands, illustrating the electronegativity of hydrogen. High reflectivity in the low frequency area induced by the impurity hydrogen is observed when only interband transitions are taken account of. A dip in reflectivity due to parallel band transitions is observed at ∼0.4 eV. Another dip at ∼4.3 eV appears when external pressure increases over 4 GPa.
  Science in China Series G Physics Mechanics and Astronomy 11/2006; 49(6):740-747. · 1.41 Impact Factor
• Article: Ab initio study of vacancies in cubic BN under pressure

  Fubo Tian, Zhiming Liu, Yanming Ma, Tian Cui, Bingbing Liu, Guangtian Zou
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  ABSTRACT: We investigate, through first-principles calculations, the pressure dependence of formation volumes and formation enthalpies of boron and nitrogen vacancies (, ) in cubic boron nitride (c-BN) using a supercell approach. We find that and have the lowest formation enthalpy and −3 and +3 can be considered as the dominant charges occurring in and at ambient pressure, respectively. And the charge states which have the lowest formation enthalpies do not change with pressure in the pressure range from 0 to 20 GPa. The formation enthalpy decreases with pressure for , while for it exhibits positive dependence of the formation enthalpy on pressure. Energy levels of defects under different pressures are also discussed. Our results suggest that for , pressure can strengthen its conductivity, while for , pressure effect is not obvious in our investigated pressure range.
  Solid State Communications 143:532-536. · 1.65 Impact Factor