For the implementation in GPUMD the potential has neither been shifted nor damped. This is important to keep in mind when using this model as it implies that both energy and force change discontinuously at the cutoff.
The implementation in GPUMD supports up to 10 atom types.
There are two parameters, which respectively control the depth (\(\epsilon\)) and the position (\(\sigma\)) of the potential well. They are given in units of eV and Å, respectively.
If there is only one atom type, the potential file for this potential model reads:
lj 1 element epsilon sigma cutoff
cutoff is the cutoff distance and
element is the chemical symbol of the element.
If there are two atom types, the potential file reads:
lj 2 <list of the 2 elements> epsilon_00 sigma_00 cutoff_00 epsilon_01 sigma_01 cutoff_01 epsilon_10 sigma_10 cutoff_10 epsilon_11 sigma_11 cutoff_11
If there are three atom types, the potential file reads:
lj 3 <list of the 3 elements> epsilon_00 sigma_00 cutoff_00 epsilon_01 sigma_01 cutoff_01 epsilon_02 sigma_02 cutoff_02 epsilon_10 sigma_10 cutoff_10 epsilon_11 sigma_11 cutoff_11 epsilon_12 sigma_12 cutoff_12 epsilon_20 sigma_20 cutoff_20 epsilon_21 sigma_21 cutoff_21 epsilon_22 sigma_22 cutoff_22
The extension to more than three atom types should be apparent from the examples above.