Interface 4-1S
Summary:
The 4-1S interface is used with potential energy subprograms for 4-body systems.
The coordinate system used is useful for systems that are dimers of two diatomic molecules.
(The 4-XS interface is designed for more general 4-body systems.)
The driver program obtains the energy at one or more
nuclear geometries by passing them as arguments between the subprogram and the driver
program.
Format and selected details:
The subroutine PREPOT, which takes no arguments, is called once
before subsequent calls to the subroutine POT. PREPOT is usually used
to initialize constant parameters of the surface, which are stored using
the FORTRAN command save. Alternatively, the parameters may be stored
in common blocks. Once the surface has been initialized, the
subroutine POT may be called whenever the potential energy is needed.
In general, a 4-1S potential energy routine has the following format:
SUBROUTINE PREPOT
DATA STORAGE/HERE/,ETC...
SAVE
RETURN
ENTRY POT( R1, R2, R, TH1, TH2, TAU, E )
E = . . .
RETURN
END
Required variables:
The subroutine POT takes the following arguments
POT ( R1, R2, R, TH1, TH2, TAU, E )
where
Throughout this discussion we will consider a
dimer of diatomics (AB)(AB) as our four-body system, although
the interface is more general. Atomic units are used throughout.
|
| R1,R2 |
input, double precision |
Diatomic internuclear distances for each dimer.
|
| R |
input, double precision |
Distance between the centers of mass of the dimers.
|
| TH1,TH2 |
input, double precision |
The angles between the AB diatom bonds and the vector
connecting the centers of mass of the two diatoms.
|
| TAU |
input, double precision |
The dihedral angle between two planes; the first plane
contains the first AB diatom bond and the vector
connecting the centers of mass of the two diatoms, and the
second plane contains the second AB diatom bond and the vector
connecting the centers of mass of the two diatoms.
|
| E |
output, double precision |
The potential energy.
|