Zheng-Zhe Lin

Statistical model for small clusters transforming from one isomer to another

Based on the fact that the kinetic energy of one atom in small cluster still obeys the Boltzmann distribution, a statistical model is developed to predict the time consumed by a small cluster transforming from one isomer to another and is tested by vast molecular dynamics simulations of C(12) isomers transformation in helium gas at high temperatures (2000-3500 K). Extrapolating the model to lower temperatures, we found that the time for the most probable isomer of C(12) formed at 2500 K turning into the most stable one is more than 10(12) years at room temperature.

Predicting the stability of nanodevices

A simple model based on the statistics of single atoms is developed to predict the stability or lifetime of nanodevices without empirical parameters. Under certain conditions, the model produces the Arrhenius law and the Meyer-Neldel compensation rule. Compared with the classical molecular-dynamics simulations for predicting the stability of monatomic carbon chain at high temperature, the model is proved to be much more accurate than the transition state theory. Based on the ab initio calculation of the static potential, the model can give out a corrected lifetime of monatomic carbon and gold chains at higher temperature, and predict that the monatomic chains are very stable at room temperature.

Controlling the electronic properties of monatomic carbon chains

Based on ab initio calculations, it is shown that the energy gap of pure monatomic carbon chains can be changed from 0.27 up to 1.42 eV when the chain is stretched by 10%, and the chains can be turned into n-type or p-type semiconductors by doping (B, N, Si, P) atoms or into rectification device by doping the BN molecule. The doping process was proved by Car-Parrinello molecular dynamics, and the lifetime of the doped chains is predicted to be about 1070 years at room temperature. The results suggest that short monatomic carbon chains are a good candidate for tunable laser medium.

High-efficient tunable infrared laser from monatomic carbon chains

Based on ab initio calculations, short B-doped monatomic carbon chains (MCCs) are suggested to serve as working medium for tunable infrared lasers. The MCCs derived from single-layer graphene in vacuum are proved to be very stable at room temperature, and their band gap is quite stretching-controllable with corresponding laser wavelength varying in the range 870–4590 nm, which is not easy to be implemented via previous techniques. High electro-optical conversion efficiency can be achieved by simply applying electric voltage on the chain ends and the MCC lasers are naturally polarized.

Theoretical prediction of the growth and surface structure of Pt and Ni nanoparticles

The surface structure of crystal grains determines the catalytic efficiency of metal particles. In this paper, we apply our recently established condensation potential model to predict the surface structure of Pt and Ni nanoparticles, which are used in fuel cells, showing the model works well but the Wulff construction fails. Based on first-principle calculations via this model, the surfaces of various shapes of Pt/Ni nanoparticles are mainly composed of fcc (111) faces (about 80%/60% of the total area). The results are consistent with existing experimental observations. Because of the simplicity of calculations, the model may be widely used to predict the surface structure of common nanoparticles.

Electronic rectification devices from carbon nanocones

The electronic rectification effects of single wall carbon nanocones (SWCNCs) with cone angles 113°, 60°, and 39° are shown by density functional theory calculation and non-equilibrium Green’s functional method, and the 113° cone owns the best rectification. Based on this result, the experiment on the rectification effects of cone-like structures is explained. To realize the rectification device, a scheme for fabricating single wall carbon nanocones standing on substrates with the controlled cone shapes is suggested and was verified via molecular dynamics simulations.

Excitation of large-scale delocalized quantum state by local interactions

It seems impossible to establish the population Rabi oscillation between two delocalized states by a resonant electromagnetic wave beam focused in a local area because the interaction information would be simultaneously propagated to every spatial point of the system, breaking relativistic causality. We examined this issue in an ideal model of a single electron moving in a one-dimensional box and in a realistic system of a monatomic carbon chain, showing that the resonant Rabi oscillation cannot be established until the initial wave package, formed by many other far-off-resonant states, transports from the interaction area crossing over all the system space. Furthermore, it is demonstrated that the two-level approximation is good when the duration of laser pumping is long enough, and if the laser interaction area is shorter than 10% of the system size, it is very difficult to pump the population of the ground state to excited ones at finite temperatures.

Ion Acceleration by the Coulomb Explosion of Graphene

Coulomb explosion of graphene with different sizes and layers is investigated via molecular dynamics simulation. A group of collimated ions with average energy of keV can be obtained from the Coulomb explosion process of nanometer-scale multilayer graphene in a tube with nanometer-scale length, as the carbon ion taking on only 1+ charge. The average ion energy is found to be proportional to the square root of the number of atoms in a single layer while also proportional to layer numbers. According to this linear relationship, we estimate that collimated ions with average energy as high as MeV can be generated from graphene layers of several microns while the carbon ions taking on 3+ charge.