As a newly developed photovoltaic technology, organic-inorganic hybrid solar cells have attracted great interest because of the combined advantages from both components. An ideal inorganic acceptor should have a band gap of about 1.5 eV and energy levels of frontier orbitals matching those of the organic polymer in hybrid solar cells. Hybrid density functional calculations are performed to search for optimal inorganic nanomaterials for hybrid solar sells based on poly(3-hexylthiophene) (P3HT). Our results demonstrate that InSb quantum dots or quantum wires can have a band gap of about 1.5 eV and highest occupied molecular orbital level about 0.4 eV lower than P3HT, indicating that they are good candidates for use in hybrid solar cells. In addition, we predict that chalcopyrite MgSnSb₂ quantum wire could be a low-cost material for realizing high-efficiency hybrid solar cells.

Hongjun Xiang;Su Huai Wei;新高 龚

Journal of Physical Chemistry C

2009

By using the recently improved generalized-simulated-annealing algorithm and the molecular dynamics method, we numerically fit an interatomic potential for lead. The potential obtained can correctly reproduce many physical properties of lead in crystalline and non-crystalline phases. The surface energy and surface relaxation obtained are in good agreement with the experimental results. The melting point predicted by this potential is very close to the experimental data. The present potential is used to study the surface melting and liquid structure; good agreement with experimental results is observed.

得彦 孙;Y. Xiang;新高 龚

Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties

1999-8

Recent experiments reveal that the honeycomb ruthenium trichloride α-RuCl3 is a prime candidate of the Kitaev quantum spin liquid (QSL). However, there is no theoretical model which can properly describe its experimental dynamical response due to the lack of a full understanding of its magnetic interactions. Here, we propose a general scheme to calculate the magnetic interactions in systems (e.g., α-RuCl3) with nonnegligible orbital moments by constraining the directions of orbital moments. With this scheme, we put forward a minimal J1-K1-Γ1-J3-K3 model for α-RuCl3 and find that: (I) The third nearest neighbor (NN) antiferromagnetic Heisenberg interaction J3 stabilizes the zigzag antiferromagnetic order; (II) The NN symmetric off-diagonal exchange Γ1 plays a pivotal role in determining the preferred direction of magnetic moments and generating the spin wave gap. An exact diagonalization study on this model shows that the Kitaev QSL can be realized by suppressing the NN symmetric off-diagonal exchange Γ1 and the third NN Heisenberg interaction J3. Thus, we not only propose a powerful general scheme for investigating the intriguing magnetism of Jeff=1/2 magnets, but also point out future directions for realizing the Kitaev QSL in the honeycomb ruthenium trichloride α-RuCl3.

Y. S. Hou;H. J. Xiang;新高 龚

Physical Review B

2017-8-7

A monolayer FeSe thin film grown on SrTiO3(001) (STO) shows the sign of Tc>77K, which is higher than the Tc record of 56 K for bulk FeAs-based superconductors. However, little is known about the magnetic ground state of FeSe, which should be closely related to its unusual superconductivity. Previous studies presume the collinear stripe antiferromagnetic (AFM) state as the ground state of FeSe, the same as that in FeAs superconductors. Here we find a magnetic order named the "pair-checkerboard AFM" as the magnetic ground state of tetragonal FeSe. The pair-checkerboard order results from the interplay between the nearest-, next-nearest, and unnegligible next-next-nearest neighbor magnetic exchange couplings of Fe atoms. The monolayer FeSe in pair-checkerboard order shows an unexpected insulating behavior with a Dirac-cone-like band structure related to the specific orbital order of the dxz and dyz characters of Fe atoms, which could explain the recently observed insulator-superconductor transition. The present results cast insights on the magnetic ordering in FeSe monolayer and its derived superconductors.

Hai Yuan Cao;Shiyou Chen;Hongjun Xiang;新高 龚

Physical Review B - Condensed Matter and Materials Physics

2015-1-26

As alternatives to the mixed-anion Cu₂ZnSn(S,Se)₄ alloys, the mixed-cation Cu₂Zn(Sn,Ge)Se₄ and Cu ₂Zn(Sn,Si)Se₄ alloys can also span a band gap range that fits the requirement of the solar cell light absorber. However, material properties of these alloys as functions of alloy composition x are not well known. In this paper, using the first-principles calculations, we study the structural and electronic properties of these alloys. We find that (i) the Cu₂Zn(Sn,Ge)Se₄ alloys are highly miscible with low formation enthalpies, while the Cu₂Zn(Sn,Si)Se₄ alloys are less miscible; (ii) the band gap of Cu₂Zn(Sn,Ge)Se₄ increases almost linearly from 1.0 eV to 1.5 eV as the Ge composition x increases from 0 to 1, whereas the band gap of Cu₂Zn(Sn,Si)Se ₄ spans a larger range from 1.0 eV to 2.4 eV and shows a slightly larger bowing; and (iii) the calculated band offsets shows that the band gap increase of the alloys with the addition of Ge or Si results primarily from the conduction band upshift, whereas the valence band shift is less than 0.2 eV. Based on these results, we expect that the component-uniform and band-gap-tunable Cu₂Zn(Sn,Ge)Se₄ and Cu ₂Zn(Sn,Si)Se₄ alloys can be synthesized and have an improved photovoltaic efficiency.

Qiang Shu;Ji Hui Yang;Shiyou Chen;冰 黄;Hongjun Xiang;新高 龚;Su Huai Wei

Physical Review B - Condensed Matter and Materials Physics

2013-3-27

The electronic structure and atomic relaxation of twin stacking faults along [111] direction in silicon are studied within the local density approximation with first principle cluster model self-consistent calculations. The atomic relaxation obtained from the view point of total energy is in agreement with experiments. The electronic structure, defect levels, and fault energy of twin stacking faults in silicon are also discussed.

新高 龚;Qing-qi Zheng Qing-qi;Ru-shan Han Ru-shan;Wei-sheng Yang Wei-sheng

Solid State Communications

1987-4

Based on a model of the melting of grain boundaries (GB), we discuss the possibility of the existence of a superheated GB state. The molecular dynamics simulation presented here shows that the superheated GB state can be realized in the high symmetric tilt GB. The sizes of liquid nuclei exceeding a critical size determined whether or not the superheating grain boundary melted. Our results also indicate that an increase of the melting point due to pressure is smaller than the superheating due to a nucleation mechanism.

Wei Fan;新高 龚

Physical Review B - Condensed Matter and Materials Physics

2005-8-1

We propose a newmultiscalemethod that couplesmolecular dynamics simulations (MD) at the atomic scale and finite element simulations (FE) at the continuum regime. By constructing the mass matrix and stiffness matrix dependent on coarsening of grids, we find a general form of the equations of motion for the atomic and continuum regions. In order to improve the simulation at finite temperatures, we propose a low-pass phonon filter near the interface between the atomic and continuum regions, which is transparent for low frequency phonons, but dampens the high frequency phonons.

Guowu Ren;Dier Zhang;新高 龚

Communications in Computational Physics

2011-11

The reactions of an O2 molecule with the neutral and positively charged Sin (n=3-16) clusters are studied with first-principles calculations. Neutral Sin (n=4,5,6,7,10,14) and charged Sin+ (n=4,5,6,7,13,15) clusters show higher inertness to O2 molecule adsorption, which is in good agreement with experimental results. Both charge transfer and hybridizations between Si and O play an important role in the dissociative adsorption of O2 molecule. We find that the spin triplet-single conversion of O2 molecule is always accompanied with O2 dissociatively chemisorbed on the Sin clusters.

S. F. Li;新高 龚

Journal of Chemical Physics

2005-5

We studied the general chemical trends of defect formation in MgTe using first-principles band structure methods. The formation energies and transition energy levels of intrinsic defects and extrinsic impurities and some defect complexes in zinc blende MgTe were calculated systematically using a new hybrid scheme. The limiting factors for p- and n-type doping in MgTe were investigated. Possible solutions to overcome the doping limitation of MgTe are proposed. The best p-type dopant is suggested to be N with nonequilibrium growth process and the best n-type dopant is suggested to be I with its doping complex V _Mg+ 4I_Te.

Ji Hui Yang;Shiyou Chen;Hongjun Xiang;新高 龚;Su Huai Wei

Physical Review B - Condensed Matter and Materials Physics

2011-6-14