| In 1959,Feynman’s vision of layered materials inspired people to explore two-dimensional materials,until the advent of graphene in 2004,the study of two-dimensional layered materials set off a boom.Compared with three-dimensional materials,two-dimensional materials are widely used in the fields of photodetectors,photocatalysis,solar cells and devices due to their large specific surface area,high carrier mobility and strong anisotropy.Especially in the past few decades,photocatalysts based on two-dimensional materials have been widely studied,such as Transition Metal Dichalcogenides,Graphitic Carbon Nitride,Hexagonal Boron Nitride,Phosphorene materials,etc.At the same time,the non-adiabatic effect has gradually attracted scientists attention and been known as an important factor affecting the properties of materials in photophysics and photochemistry.In order to predict the photocatalytic properties of two-dimensional materials more comprehensively,we not only study the basic photocatalytic properties of two-dimensional materials by using the simulation method of first-principles calculation,but also further investigate the influence of the adiabatic effect on the excited carrier dynamics by using the mixed quantum and classical non-adiabatic molecular dynamics methods.Compared with experiments,this simulation method has the advantages of low cost,high efficiency and high security.We have designed two-dimensional M2Se2(M=Al,Ga,In)and Ge2As4S2 monolayer,and their excellent stability and good photocatalytic performance were predicted by first-principle calculations.Meanwhile,the electron-hole recombination dynamics of Ge2As4S2 monolayer was simulated by non-adiabatic molecular dynamics.The following two aspects are mainly studied and the corresponding results are obtained:1.Based on the first principles and density functional theory,the photocatalytic properties of 2D M2Se2(M=Al,Ga,In)materials were studied after their stable configuration obtained.Through the molecular dynamics simulation based on the adiabatic approximation,it is found that they are stable at room temperature and high temperature;and then their work functions and cohesive energies were calculated and compared with phosphorene.It is proved that they have both chemical stability and energy stability.The band structures of M2Se2(M=Al,Ga,In)materials indicate they are indirect bandgap semiconductors by using the hybrid functional.And their bandgap values and the edge positions after applying a small strain all meet the conditions of photocatalytic hydrolysis for hydrogen production.At the same time,we also find that proper strain can enhance the material’s absorption of visible light.Finally,through the deformation potential theory,we get that the carrier mobility of the two-dimensional M2Se2(M=Al,Ga,In)material can reach 104 cm2V-1s-1,which is higher than that of silicon.The above results have indicated that the two-dimensional M2 Se2(M=Al,Ga,In)materials have good photocatalytic performance,and could be applied in the field of photoelectricity and photocatalysis.2.Based on density functional theory,we studied the basic photocatalytic properties and non-adiabatic effect of Ge2As4S2 monolayer.It is obtained by adjacent element substitution of GeP3 and has a similar crystal structure to that of GeP3.Using the VASP software package to optimize the Ge2As4S2 monolayer,the stable configuration was obtained,and further,the simulations of ab initio molecular dynamics,cohesive energy and work function were carried out.The results show that Ge2As4S2 monolayers have a stable structure.Based on first-principles calculations,we investigate the electronic properties,optical properties,carrier mobility,and strain engineering of Ge2As4S2 monolayers.The results show that the Ge2As4S2 monolayer is a direct bandgap semiconductor with ideal bandgap value,band edge position and high absorption coefficient of visible light.Its carrier mobility is as high as 106 cm2V-1s-1.And the strong anisotropy between different charges in different directions is beneficial to the separation of electrons and holes.In order to further understand the process of electron-hole recombination dynamics,we use the method of non-adiabatic molecular dynamics to obtain the intensity of non-adiabatic coupling and carrier lifetime of Ge2As4S2 monolayer.It is found that the process of electron-hole recombination between the top of the valence band and the bottom of the conduction band is relatively slow,and the lifetime of photogenerated carriers is fairly long.It’s beneficial to improve the efficiency of photocatalysis,realize photocatalysis and so on in the field of application. |
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