Study Of Several Factors Effect On The Construction Of Interatomic Potentials

Interatomic potentials are the important method to research materials in the microscopic scale, and they are the basis of computer simulation like molecular dynamics. Firstly, we must choose the appropriate interatomic potentials for molecular dynamics simulation to determine the strength of interparticle force. And then we can get the phase space trajectory of molecular dynamics simulation to research the macroscopic property of the materials. It is thus clear that, reasonableness or not of interatomic potentials affects the reliability and accuracy of the further simulation results directly. That we can't find appropriate interatomic potentials is the major reason which limits the application of computer simulation like molecular dynamics. Thus it is important for the theory and practice significance to construct reasonable and reliable interatomic potentials.Interatomic potentials are depended on the properties of materials. For the pair potential, it has an easy transportability, for the n-body potential, it has the poorer transportability. That reason is mainly that when the environment which around the atoms is changed will has an greater influence on the n-body interaction. However, when the pair potential is applied in the actual material, there will be two obvious shortcomings, one is that the cauchy relation will appears, which is not exist in the actual material, another is that if we assume the cauchy relation is true, it will cause an unreasonable phenomena that the vacancy formation energy is equal to cohesive energy. Therefore, it is a very significance work to construct an appropriate n-body potentials for material.It is a complex project to construct interatomic potentials, it includes model selection, parameters determination, interatomic potentials test, correction interatomic potentials and the other links. Getting a relatively satisfactory interatomic potentials is restricted by many factors, such as cutoff processing, how much input parameters, difficulty of the fitting process, the influence of the structure stability with the form of the interatomic potentials and the application scope of the interatomic potentials, etc. Taking NiAl alloy, for example, an embedded-atom potential is constructed for the interatomic potential of NiAl alloy. NiAl alloy is an high-temperature structural material, and it has many excellent performances, also it is a development potential alloy material. This treatise is paid attention to study the influence of NiAl alloy potential that caused by cutoff, stiffen, and the choice of the interatomic potential forms. The results show that: when we select the polynomial form of the pair potential, cutoff distance can be only chose between second and third neighbor, or the fourth and fifth neighbor, but not between the third and fourth neighbor or the fifth and sixth neighbor. When we superposed a function onto the primitive function for cutoff processing, the scope of the superposition function cannot be too big, otherwise, it will affect the calculated result of cohesive energy and vacancy formation energy. When Using the form of the function that contain the cutoff item, the problems will not be exist.This treatise will also test the NiAl alloy interatomic potential that construct. First, examining the interatomic potential in the structure stability properties, the results show that when the NiAl alloy interatomic potential is used for bcc structure, it has the lowest energy, which is agreed with the practical situation. Second, comparing the interatomic potential curve to the one of Smith and Rose cohesive, they are in excellent agreement, which shows that the interatomic potential also have the good performance in non-equilibrium.