# Potential File Format 4

## Format specification

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

As with potential files in format 3 each data column has its own spacing. But with potential format 4 the requirement that the sampling points be equidistant is dropped. Arbitrarily spaced sampling points are possible, but the sampling points have to be given in ascending order.

##### Header

All potential files need a header block at the beginning, which is described in detail here: Potential files.

##### Sampling points block

Preceding the data columns is a block with one line per potential, containing the number of sampling points in the corresponding potential.

Here is an example for a pair potential for two atom types, which requires three potential functions:

## last header line #E 15 15 15

##### Function tables

Seperated by blank lines then the data columns follow. Each of the tables has the form

r_0 f(r_0) r_1 f(r_1) ... r_steps f(r_steps)

Please note that $r_0 < r_1 < \ldots < r_{steps}$ is required. The order of the columns is the same as with format 3.

Similarly as for format 3, 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.

If the `#G`

header line is specified, each function table 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.

## Examples

A sample format 4 potential file for a binary system (EAM potential) is available
here (with the `#G`

header line).

And here is a very simple pair potential for a monoatomic system. All lines starting with `##`

are comments and can be removed.

## This is the header ## F -- this is the Format line ## 4 -- this is the Format number ## 1 -- this is the number of potentials in this file #F 4 1 ## E -- this is the End of the header #E ## Sampling points block ## There needs to be one line with the number of sampling points for each potential (1 in this example) 14 ## Function tables ## One function table for each potential (1 in this example) ## The number of lines must be equal to the number provided in the respective line in the distance block (14 in this example) ## Each line has two values, the distance and the potential value ## The first and the last line define the range of the potential 2.7785714285714285e+00 8.4255614529302880e-01 3.2571428571428571e+00 2.0271471509245159e-01 3.7357142857142858e+00 2.2155522312087100e-02 4.2142857142857144e+00 -6.8303638148139376e-02 4.6928571428571431e+00 -4.9043278969706922e-02 5.1714285714285717e+00 -1.0946697911942214e-02 5.6500000000000004e+00 -1.0298525723152156e-02 6.1285714285714290e+00 -6.5685589306463460e-03 6.6071428571428577e+00 -2.0283626156443295e-03 7.0857142857142854e+00 1.2197714420628298e-02 7.5642857142857141e+00 2.2148801387662245e-02 8.0428571428571427e+00 1.4461939319528331e-02 8.5214285714285722e+00 9.9020972820913523e-03 9.0000000000000000e+00 0.0000000000000000e+00