The files asp-w2.defn and asp-w4.defn are potential definition files for the ASP-W2 and ASP-W4 potentials as described by Millot, Soetens, Martins Costa, Hodges and Stone in J. Phys. Chem. A (1998) 102, 754-770. To use them you need the Orient program.

The complete data file will look something like the following:

Variables
x1 0.0 A
Note (x1,y1,z1) is the position of water molecule 1.
Note A means Angstrom. Use B for bohr.
y1 0.0 A
z1 0.0 A
alpha1 0.0 D
Note (alpha1, beta1,gamma1) are the Euler angles for molecule 1.
Note D means degrees.
beta1 0.0 D
gamma1 0.0 D
x2 0.0 A (Similarly for molecule 2)
y2 0.0 A
z2 3.0 A
alpha2 0.0 D
beta2 0.0 D
gamma2 0.0 D
End

Note now read the stuff in the definition file:
#include asp-w2.defn

Note Now do whatever calculations you want. For example:

Energy

Minimize
frequencies
End

Finish

This data file would calculate the energy at the starting geometry, and then find a local minimum.

If you want to obtain energies to use in your own program, proceed as follows:

1. Download the Orient program and compile it. (See the instructions that come with the program distribution.)
2. At the beginning of your program, include the statement
   call orient
   This will call the main routine (called orient) of the Orient program, which will read in the data file as far as the "finish" line and return to your program. If you specify any calculations (as in the example above) they will be carried out, but it is not necessary to do so.
3. Whenever you want to calculate the energy, use the statement
   call energy(values,es,er,eind,edisp,etotal)
   The array values should contain values for the variables defining the geometry (i.e. x1, y1, z1, etc.) in the order that you defined them. The numbers must be in internal coordinates (bohr for distances, radians for angles), whatever units you used in the original definition. The routine will return the electrostatic, repulsion, induction and dispersion energies in the variables es, er, eind and edisp, and their total in etotal. All in double precision.
4. You will need to link all the Orient object files with your program except the file run_orient.o, which is a trivial main program that normally just calls the orient routine and exits. The simplest way to construct the object files is to run the Makefile that comes with the program.
5. You will probably find it helpful to read the Orient program manual, included with the program distribution, even if you only want to calculate energies as described here.

This file is maintained by Anthony Stone, and was last updated on 18 February 2005.