Interface 4-XS

Summary:

The interface 4-XS is a standard interface for a 4-body system, where common blocks are used to pass data between the calling routine and the potential energy routine. The 4-XS calling protocol is the most general 4-body calling protocol in POTLIB-online. The 4-1S interface may be more convenient for systems that are dimers of diatomic molecules.

The potential energy (and possibly the derivatives) are calculated for a single geometry for each call to POT. The subroutine POT requires no arguments. The common block PT1CM is required by the POT subroutine; this common block is used to pass the geometry of the system from the calling program to the potential routine and to return the electronic state energy and derivatives to the calling program. There are several other optional common blocks that may be used to further refine calls to POT. This interface may be used with or without derivatives.

The 4-XS calling interface protocol was added to POTLIB-online on May 7, 2003.

Format and selected details:

The following common blocks are used to pass control variables and data to and from the potential subroutine.
SUBROUTINE POT

      COMMON /PT1CM/ R, ENGYGS, DEGSDR
      DIMENSION R(N3ATOM), DEGSDR(N3ATOM)

      COMMON /INFOCM/ CARTNU,INDEXES,IRCTNT,NATOMS,ICARTR,MDER,MSURF,REF
      DIMENSION CARTNU(NATOM,3),INDEXES(NATOM)

      COMMON /USRICM/ CART,ANUZERO,NULBL,NFLAG,NASURF,NDER
      DIMENSION CART(NATOM,3),NULBL(NATOM),NFLAG(20),NASURF(ISURF+1,ISURF+1)

      COMMON /USROCM/ PENGYGS,PENGYES,PENGYIJ,DGSCART,DESCART,DIJCART
      DIMENSION PENGYES(ISURF),PENGYIJ(JSURF),DGSCART(NATOM,3),
     +               DESCART(NATOM,3,ISURF),DIJCART(NATOM,3,JSURF)

      COMMON /PT3CM/ EZERO(ISURF+1)
      DIMENSION EZERO(ISURF+1)

      COMMON /PT4CM/ ENGYES,DEESDR
      DIMENSION ENGYES(ISURF),DEESDR(N3ATOM,ISURF)

      COMMON /PT5CM/ ENGYIJ,DEIJDR
      DIMENSION ENGYIJ(JSURF),DEIJDR(N3ATOM,JSURF)

    ENGYGS  = ENERGY AS SOME FUNCTION OF R . . . 
    DEGSDR(:) = . . . 

RETURN

END

A detailed description of the common blocks is provided in:

R. J. Duchovic, Y. L. Volobuev, G. C. Lynch, D. G. Truhlar, T. C. Allison, A. F. Wagner, B. C. Garrett, and J. C. Corchado, "POTLIB:   A Potential Energy Surface Library for Chemical Systems", Computer Physics Communications 144, 169-187 (2002).
The common block PT1CM is the only common block that is always required.
COMMON /PT1CM/ R, ENGYGS, DEGSDR
DIMENSION R(N3ATOM), DEGSDR(N3ATOM)

R(N3ATOM) input, real*8 An array of the N3ATOM internuclear bond distances.

ENGYGS output, real*8 The computed potential energy.

DEGSDR(N3ATOM) output, real*8 The computed derivatives with respect to the N3ATOM internuclear distances. This field is included even when derivatives are not available.