Chen Xiang-Rong

First-principles calculations for elastic properties of rutile TiO2 under pressure

This paper studies the equilibrium structure parameters and the dependences of the elastic properties on pressure for rutile TiO2 by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density functional theory. The obtained equilibrium structure parameters, bulk modulus B0 and its pressure derivative B0 are in good agreement with experiments and the theoretical results. The six independent elastic constants of rutile TiO2 under pressure are theoretically investigated for the first time. It is found that, as pressure increases, the elastic constants C11, C33, C66, C12 and C13 increase, the variation of elastic constant C44 is not obvious and the anisotropy will weaken.

Distribution of vibrational energy levels of protein molecular chains

The distributions of the quantum vibrational energy levels of the protein molecular chain are found by the discretely nonlinear Schrodinger equation appropriate to protein obtained from the Davydov theory. The results calculated by this method are basically consistent with the experimental values. Furthermore, the energy spectra at high excited states have also been obtained for the molecular chain which is helpful in researching the properties of infrared absorption and Raman scattering of the protein molecules.

Nonlinearly vibrational energy-spectra of molecular crystals*

The nonlinear quantum vibrational energy spectra of amide-I in the molecular crystals acetanilide are calculated by using the discrete nonlinear Schrodinger equation appropriate to this kind of crystals. The numerical results obtained by this method are in good agreement with the experimental values. Meanwhile, the energy levels at high excited states have also been obtained for the acetanilide, which is helpful in researching the Raman scattering and infrared absorption properties of the this kind of crystals.

Elastic Properties of Rutile TiO2 at High Temperature

Dependence of elastic properties on temperature for rutile TiO2 is investigated by the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density function theory (DFT) and the quasi-harmonic Debye model. The six independent elastic constants of rutile TiO2 at high temperature are theoretically obtained for the first time. It is found that with increasing temperature, the elastic constants will decrease monotonically. Moreover, we successfully obtain the polycrystalline moduli B-H and G(H), as well as the Debye temperature Theta(D).

Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations

The pressure induced phase transitions of RuB(2) from the OsB(2)-type structure to the ReB(2)-type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient approximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB(2)-type RuB(2) to the ReB(2)-type RuB(2) at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Gruneisen parameter on pressure and temperature for OsB(2)-type RuB(2) and ReB(2)-type RuB(2) are also investigated.

Pseudopotential Density-Functional Calculations for Structures of Small Carbon Clusters CN (N = 2 ~ 8)*

We introduce a first-principles density-functional theory, i.e. the finite-difference pseudopotential density-functional theory in real space and the Langevin molecular dynamics annealing technique, to the descriptions of structures and some properties of small carbon clusters CN (N = 2 ~ 8). It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.

Application of shell model in molecular dynamics simulation to MgO

The P-V-T equation of state of MgO has been simulated under high pressure and elevated temperature using the molecular dynamics (MD) method with the breathing shell model (BSM). It is found that the MD simulation with BSM is very successful in reproducing accurately the measured molar volumes of MgO over a wide range of temperature and pressure. In addition, the MD simulation reproduces accurately the measured volume compression data of MgO up to 100GPa at 300K. It is demonstrated that the MD simulated P-V-T equation of state of MgO could be applied as a useful internal pressure calibration standard at elevated temperatures and high pressures.

Vibrational energy-spectra and infrared absorption of alpha-helical protein molecules

The quantum energy spectra, including high excited states, of vibrational amide-I or of intramolecular excitations in α-helical protein molecules, are calculated by the discrete nonlinear Schrodinger equation together with the parameters appropriate to the systems. The distribution of energy levels obtained is basically consistent with the experimental values obtained by infrared absorption and Raman scattering. Utilizing the energy spectra we explain the laser Raman spectrum from metabolically active escherichia coli and we present some further features of the infrared absorption of the protein molecules.

Effects of Contact Geometry on the Transport Properties of a Silicon Atom

Contact geometry and electronic transport properties of a silicon atom sandwiched between Au electrodes in three different anchoring configurations are investigated by using the density functional theory combined with the non-equilibrium Green function method. We simulate the nanoscale junction breaking process and calculate the corresponding cohesion energy, obtain the equilibrium conductance and the projected density of states of junctions in an optimal postion. We also calculate the conductance and the current of junctions at the equilibrium position under small bias voltage. It is found that all junctions have large conductance and show a linear I—V relationship, but the current and conductance of a hollow-hollow configuration is always the biggest under the voltage range of −1.2 V~1.2V. The calculated results proved that the coupling morphology of a silicon atom connected with electrodes has an important effect on the electronic transport properties of the nanoscale junction.

Electron Transport through a Silicon Atomic Chain

The electron transport properties of a silicon atomic chain sandwiched between Au (100) leads are investigated by using the density functional theory combined with the non-equilibrium Greens function method. The breaking process of Au-Si4-Au nanoscale junctions is simulated. The conductance and the corresponding cohesion energy as a function of distance dz are obtained. With the increase of distance, the conductance decreases. When dz = 18.098 A, there is a minimum value of cohesion energy. The nanoscale structure of junctions is most stable, and the equilibrium conductance is 1.71G0 (G0 = 2e2/h) at this time. The I—V curves of junctions at equilibrium position show linear characteristics.