An improved smoothed molecular dynamics method by alternating with molecular dynamics

Abstract

Abstract An effective method for nano-mechanics is presented by combining smoothed molecular dynamics (SMD) method and molecular dynamics (MD) method. SMD method was proposed in our previous work to sharply increase the feasible time step of MD. A set of background mesh was introduced in SMD and the equations of motion are solved on the background mesh nodes rather than on atom sites as in MD, which converts the controlling factor of critical time step size to the background mesh size. Much larger time step size, which can be one order larger than MD step size, can be adopted in SMD computation. But the application of SMD into problems with moving atom disorders and at finite temperature is still not satisfactory. An improvement scheme is proposed in this paper by alternating SMD computation and MD relaxation in the solution process. SMD is used at the beginning of the computation, then it is converted to MD relaxation whenever required. SMD computation continues after MD relaxation until next relaxation is needed. The conversion between MD and SMD is very convenient and straightforward owing to their similarities. The accuracy can be guaranteed by MD relaxation process, and the overall efficiency is better than MD efficiency since large time step size can be adopted in SMD computation. Examples of nano-indentation and nanowire tension validate the alternating SMD method. Influences of factors including the length of relaxation intervals and the number of MD relaxation steps are studied. A criterion automatically determining the alternating process is also proposed and validated.