GEOMETRY
Externprogram externprog.exe coord=coords.inp
energy=energy.out grad=grads.out
..
END
Externprogram
Expert option, can only be used in combination with the new branch. Subkey EXTERNPROGRAM has been added to to allow energies and gradients to be calculated by an external program for use in a geometry optimization.
Note that you need to supply information about atomic fragments, such as the basis set, even though these are not actually used in the calculations.
When ADF is ready to perform an energy and gradient calculation, it writes the current cartesian coordinates to the file name given in the input. The format is similar to the ATOMS block in the ADF input file: it has one atom per line, with the element symbol given, followed by the x, y, and z coordinates.
ADF will then run the executable program, and then read in the energy and gradients from the file names given in the input file. The external program is thus responsible for reading the coordinates (in atomic units) written by ADF from file, generating the corresponding energy and gradients (in atomic units), and writing these to the appropriate files. ADF will then take another geometry step, and the process will repeat.
