Add force

[brucefan1983]

• Usage 1:

add_force <group_method> <group_id> <fx> <fy> <fz>

This will add constant force with components fx, fy, and fz to a group of atoms.

• Usage 2:

add_force <group_method> <group_id> <add_force_file>

add_force_file format:

<number_of_steps>
fx_0 fy_0 fz_0
fx_1 fy_1 fz_1
fx_2 fy_2 fz_2
fx_3 fy_3 fz_3

The forces in the file will be used repeatedly during the run.

• This is the first keyword in GPUMD that can be used more than once within a run.