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The calculations of two - dimensional material structure of germanene and the adsorption of gas molecules (such as CO, CO2, N2) on germanene are performed by using density functional theory. The results show that germanene has zero-band gap energy and non-spin polarized characteristics. The adsorption of gas molecules on the surface of germanene plays a role in the tunable band gap. The adsorption energy of CO is lower than that of CO2 and N2, indicating that CO is more easily to be absorbed by the other two gases. This result makes germanene a potential candidate for CO adsorption devices, contributing to the reduction of the amount of CO in the air to create a clean beautiful environment.

In this work, we have investigated the structural and electronic properties of both bulk and monolayer MoS2 based on the density functional theory (DFT) implemented in the CASTEP of Materials Studio package. The calculations are performed with the local density approximation (LDA) and generalized gradient approximation (GGA) functionals for crystal structure optimization and band structure of MoS2 bulk and monolayer. Our calculations show that the GGA functional calculated excellent band gap for bulk MoS2, while LDA functional is found to perform better for band gap calculations of a monolayer. The influence of composition in the energy bands has been realized by analyzing the partial density of states (PDOS) of each atom and density of states (DOS). By reducing the layer thickness from bulk to monolayer, it is found that band structure has the transitions from indirect band gap in the bulk MoS2 (1.53 eV) to direct band gap in the monolayer (1.82 eV). On the other hand, the charge density difference along z-direction shows that the major charge transfer occurs on the surface of the S atoms and there is a little accumulation around the surface of the Mo atoms. This property highlights the promising of MoS2 in improving the fabrication of optoelectronic devices in the future.

Molecular dynamics simulations of Cu80Ni20 (Cu:Ni = 8:2) model with the size of 8788 atoms have been carried out to study the structure and mechanical behavior at high pressure of 45 GPa. The interactions between atoms of the system were calculated by the Quantum Sutton-Chen embedded-atom potentials. The crystallization has occurred during the cooling process with a cooling rate of 0.01 K\ps. The temperature range of the phase transition is determined based on the sudden change of atomic potential during the cooling process. There is also a sudden change in the number of individual atoms in the sample. At a temperature of 300 K, both Ni and Cu atoms are crystallized into the face-centered cubic (FCC) and the hexagonal close-packed (HCP) phases, respectively. The mechanical characteristics of the sample at 300 K were also analyzed in detail through the determination of elastic modulus, number of atoms, and void distribution during the tensile process.