About problems in pair_style table command

I am using Pair_style table command to input energy force force relations with r. I use exponential potential(experimentally obtained)+LJ 12-6 for atom pair. I used different fitting method such as linear, bitmap, spline, lookup but after fitting, i check the fitting data by pair_write command which differ abnormally from the initial data table. How, i can get almost same data after fitting with slight error. As a result, my simulation does not work. Please inform me about the problem.

Best regards

The pair_style table doc page explains that you can get bad fits
with some settings, particularly if your potential is very steep
in some regions (e.g. close to the origin). I suggest you follow
the advice llisted on that page:

Here are some guidelines for using the pair_style table command to best effect:

  • Vary the number of table points; you may need to use more than you think to get good resolution.
  • Always use the pair_write command to produce a plot of what the final interpolated potential looks like. This can show up interpolation “features” you may not like.
  • Start with the linear style; it’s the style least likely to have problems.
  • Use N in the pair_style command equal to the “N” in the tabulation file, and use the “RSQ” or “BITMAP” parameter, so additional interpolation is not needed. See discussion below.
  • Use as large an inner cutoff as possible. This avoids fitting splines to very steep parts of the potential.