minimize with fix addforce

Dear all,

I want to run NEB calculations on a slab which is shear strained. And I want to do it for different strains so I want to use a loop.

To strain my system, I am using fix addforce. But I am not able to run NEB minimization (or a simple minimization) with that fix.

I am adding the keyword energy with a variable which defines the extra energy coming from the extra force.

But I get the error “ERROR: Variable for fix addforce is invalid style” so I am apparently not doing it the proper way.

Here is my scrpit in which instead of running an NEB I just carry out a simple minimization (to simplify the problem):

Dear all,

I want to run NEB calculations on a slab which is shear strained. And I
want to do it for different strains so I want to use a loop.

To strain my system, I am using fix addforce. But I am not able to run NEB
minimization (or a simple minimization) with that fix.
I am adding the keyword energy with a variable which defines the extra
energy coming from the extra force.
But I get the error "ERROR: Variable for fix addforce is invalid style" so
I am apparently not doing it the proper way.

​no, you need to do the energy computation for each atom individually with
an atom style variable, as indicated by the quote from the fix addforce
documentation below:

Note that when the *energy* keyword is used during an energy minimization,
you must insure that the formula defined for the atom-style *variable*
<http://lammps.sandia.gov/doc/variable.html> is consistent with the force
variable formulas...​

​axel.​