“how can I do this”

Hi,
I have problem in simulate with Qeq command.
In the Reax examples, I find that the charge column of all the data files is 0 (in data file). But in other examples (Qeq/point or ....) I find the charge column of atoms related to atom types. 
So, does it means that defining the charges of  atoms for Qeq/reax in advance has no impact on the simulation? and defining the charges of  atoms for Qeq/point or Qeq/Fire or .. has impact on the simulation?

In another words, the intial charges of  atoms (in data file) for Qeq/point or Qeq/Fire or Qeq/shielded has impact on the simulation?

regards
reza

Hi,
I have problem in simulate with Qeq command.
In the Reax examples, I find that the charge column of all the data files is 0 (in data file). But in other examples (Qeq/point or ....) I find the charge column of atoms related to atom types. 
So, does it means that defining the charges of  atoms for Qeq/reax in advance has no impact on the simulation? and defining the charges of  atoms for Qeq/point or Qeq/Fire or .. has impact on the simulation?

what do you mean exactly by “impact on the simulation”?

yes, there is an effect. but no, it should not result in significantly different simulations. the initial charges can help to initialize the charge equilibration and thus can significantly speed up the first call to fix qeq/*. in ambiguous cases, it may even help to guide QEQ to better find the desired minimum and not get trapped in an undesired one. but by and large, it should converge to the same state and thus result in equivalent trajectories.

as you may know, MD is chaotic, and thus you have to deal with the so-called “butterfly effect”, i.e. the tiniest of differences (including rounding errors for floating point math) will grow exponentially, and thus simulation trajectories will eventually diverge exponentially. having different initial charges for QEQ calculations, may accelerate that. but that does not affect the correctness of those calculations any less than using a different number of processors, or using a multi-threaded or GPU accelerated version of a pair style.

axel.