extforce -define an external force on an atom
SYNOPSIS
extforce atom1 fx fy fz
[dfx dfy dfz]
extforce atom1 atom2 f [df]
DESCRIPTION
The extforce command defines an external force on an atom and adds it to the list of external forces. The list of external forces can be printed using the list_extforces command. A force in an arbitrary direction can be applied on atom1 using
extforce atom1 fx fy fz
A force of magnitude f on atom1 in the direction of atom2 can be defined using
extforce atom1 atom2 f
A rate of change of the force can be specified using dfx dfy dfz, or df. The force is updated at each step as
fx = fx + dfx * dt
fy = fy + dfy * dt
fz = fz + dfz * dt
Forces and rates of change must be specified in atomic units.
EXAMPLE
To add a repulsive force of magnitude 0.01 between atoms A and B, keeping the total force on the center of mass zero, use
extforce A B -0.01
extforce B A -0.01
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