There are two kinds of potential energy surface subroutine interfaces in Section One:

(1)Molecular mechanics interfaces, which allow for a variable number of atoms and are labeled

T-MM-Dwhere

T= "HO" or "HE" for a homonuclear or heteronuclear potential energy subroutine, respectively, MM stands for "molecular mechanics", andDis the number of analytic derivatives available.

The following molecular mechanics interface is currently standard in POTLIB: HO-MM-0, HO-MM-1.

More interfaces will be added as new potential energy subroutines become available.

(2)Interfaces for a fixed number of atoms. These interfaces are labeled

N-DMwhere

Nis the number of bodies,Dis the number of analytic derivatives available plus one (e.g., forD= 1, only the potential energy is available, forD= 2, the potential energy and the first derivatives are available), andMis S for scalar mode (i.e., the energy for one geometry is computed per subroutine call, and the geometries, energies, and derivatives (when available) are passed using common blocks) and V for vector mode (i.e., the energies and derivatives (when available) for an array of geometries are calculated per subroutine call and are passed as arguments). Note ifD= X, the potential interface is general enough to handle more than one value ofD.

The following interfaces for a fixed number of atoms are currently standard in POTLIB: POTLIB-2001, 3-XS, 3-1V, 3-2V, 4-XS, 4-1S, 5-1S, 6-1S, and 7-1S.

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