The potential formats 3 and 4 are used for tabulated potentials. Format 3 implicitly assumes equidistant sampling points for the potential function tables and supports all header lines.

In a potential file in format 3, each data column has its own range and spacing. Sampling points are equidistant in the atomic distance r or (when using EAM-type interactions) electron density n. If we have n data columns, the file starts with n lines of the form

x_begin x_end steps

specifying the start, end, and the number of function values in each data set. n data columns. The argument x is either the atom distance, or the host electron density. These n lines are then followed by n blocks with the function values, one for each atom type pair or atom type. The spacing of function values is computed from the begin, end, and number of function values of the corresponding table and can be different for the different data columns.

If the #G header line is specified, each data block must be preceded by two values specifying the gradient of the function at the lower and upper boundaries. A value of $10^{30}$ or greater triggers the usage of natural splines (curvature 0 at boundaries). You should not make the gradient variable at boundaries where natural splines are specified. This will lead to undesired results.

For potential functions that are a function of distance (e.g. pair potentials, EAM transfer functions), a smooth cutoff at the final sampling value is assumed and the value is not varied.

A sample format 3 potential file for a binary system for an EAM potential is available with or without the #G header line.