specifying virtual atoms

[rfhari]

Hello, I am working on implementing the Virtual Crystal Approximation (VCA) in molecular dynamics simulations for alloys, such as the Al(x)Ga(1-x)N system. I've interpolated the second- and third-order force constants (FC2 and FC3) based on the Al composition to use as inputs. My plan was to utilize the Force Constant Potential (FCP) to run a short MD simulation on virtual crystal and compare the forces obtained from the interpolated FC2 and FC3 with those from a fully disordered system.

However, I encountered an issue: FCP seem to require a list of atoms involved in the force constant calculations to be specified in the driver file. In the VCA, these atoms are "virtual" atoms, with linearly interpolated mass between Al and Ga. Could you please advise if there’s a way to incorporate such virtual atoms by modifying their mass in the equilibrium position file?

Thank you!

[brucefan1983]

I am not familiar with VCA. The equilibrium position file does not have information on mass. Mass is set in the model.xyz file via the properties=mass:R:1 tag. Can this solve your problem?

model.xyz file format:

https://gpumd.org/gpumd/input_files/model_xyz.html#model-xyz