Chunmei Tang

The geometric, optical, and magnetic properties of the endohedral stannaspherenes M@Sn12 (M=Ti, V, Cr, Mn, Fe, Co, Ni)

The geometric, optical, and magnetic properties of the M@Sn(12) clusters (M=Ti, V, Cr, Mn, Fe, Co, Ni) are studied using the relativistic density-functional method. The geometric optimization shows that the ground states of these clusters are probably very close to the I(h) structure. Our calculations demonstrate that the optical gaps of the M@Sn(12) can be tuned from infrared to green, and the magnetic moments of them vary from 2 mu(B) to 5 mu(B) by doping d transition metal atoms into Sn(12) cage, suggesting that M@Sn(12) could be a new class of potential nanomaterials with tunable magnetic and optical properties.

STRUCTURAL, ELECTRONIC, MAGNETIC, AND OPTICAL PROPERTIES OF 3d TRANSITION METAL ENDOHEDRAL M@Ge12H12(M=Sc–Ni) CLUSTERS

The fulerine-Ni@Ge12H12 structure, which composes of four pentagons and four rhombi and is like a fullerene, has a closed-shell electronic structure, the largest HOMO–LUMO energy gap, the highest vertical ionization potential, and the lowest vertical electron affinity. All of these properties are characteristic of a magic cluster, therefore, we strongly suggest fulerine-Ni@Ge12H12 should be a magic cluster and promising as building blocks in developing cluster-assembled nanomaterials. This can be interpreted by the weak interaction between Ni and the cage together with the transference of two electrons from the 4s orbital to the 3d orbital of Ni. The magnetic moment of fulerine-M@Ge12H12(M=Sc–Ni) varies from 0 to 3 μB, implying they have potential applications in developing new nanomaterials with tunable magnetic properties. The calculated TDDFT optical properties of fulerine-M@Ge12H12(M=Sc–Ni) can be tuned broadly in the ultraviolet–visible region. This is very important for optoelectronic applications.

Dynamical energy equipartition of the Toda model with additional on-site potentials*

We study the dynamical energy equipartition properties in the integrable Toda model with additional uniform or disordered on-site energies by extensive numerical simulations. The total energy is initially equidistributed among some of the lowest frequency linear modes. For the Toda model with uniform on-site potentials, the energy spectrum keeps its profile nearly unchanged in a relatively short time scale. On a much longer time scale, the energies of tail modes increase slowly with time. Energy equipartition is far away from being attached in our studied time scale. For the Toda model with disordered on-site potentials, the energy transfers continuously to the high frequency modes and eventually towards energy equipartition. We further perform a systematic study of the equipartition time t eq depending on the energy density e and the nonlinear parameter α in the thermodynamic limit for the Toda model with disordered on-site potentials. We find , where . The values of a and b are increased when increasing the strengths of disordered on-site potentials or decreasing the number of initially excited modes.

Dynamical thermalization of Frenkel-Kontorova model in the thermodynamic limit.

We study numerically the process of dynamical thermalization in the Frenkel-Kontorova (FK) model with weak nonlinearity. The total energy has initially equidistributed among some of the lowest frequency linear modes. It is found that the energy transfers continuously to the high-frequency modes and finally evolves towards energy equipartition in the FK model. However, the metastable state, which was found in Fermi-Pasta-Ulam (FPU) model and φ(4) model in a relatively short time scale, is not found in the FK model. We further perform a very accurate systematic study of the equipartition time T(eq) as functions of the particle number N, the nonlinear parameter β, and the energy density ɛ. In the thermodynamic limit, the dependence of T(eq) on β and ɛ is found to display a power law behavior: T(eq)∝β(a)ɛ(b). The exponents a and b are numerically found to be approximately -2.0 and 1.43. This scaling law is also quite different from those of the FPU-β model and φ(4) model.

Research of Novel Circular Grating

Given that most of the optical systems are circularly symmetric, the Circular Dammann grating has wide application. However, its parameters’ design is a hard problem which restricts its development. This paper presents a new method to optimize the design of Circular Dammann grating with introducing quantum genetic algorithm and some appropriate revises. Compared with other design methods, it has obvious advantages. At the end of this paper, the simulation results are given.