The Parametric Molecular Electrostatic Potential of Wang and Ford [45,46] is generated. When PMEPR is used, extra data must follow the Z-matrix and symmetry data. This extra data defines the plane in which the electrostatic potential is plotted, and is summarized in the Table. Other keywords, e.g., MINMEP(to print the minima) or PRTMEP(to write data for esplot to use) must be present.

Table:

Data Required by PMEPR

Name of

Allowed Values

Datum

ICASE

1, 2, 3

N1

1-NUMAT

N2

1-NUMAT, not N1

N3

1-NUMAT, not N1 or N2

X0

Any real number

The various planes which can be drawn through the system are identified by the datum ICASE:

ICASE=1

If X0 is zero, then the plane generated passes through atoms N1, N2 and N3. Obviously, these atoms should not lie on a straight line. If X0 is non-zero, then the plane is parallel to the plane of atoms N1, N2 and N3, but X0 Ångstroms above it.

ICASE=2

If X0 is zero, then the plane generated is perpendicular to the plane of N1, N2 and N3, and includes the line from atom N1 to N2. If X0 is non-zero, then the plane is perpendicular to the plane of N1, N2 and N3, and is X0 Ångstroms above, and parallel to, the line from atom N1 to N2.

ICASE=3

The plane used is that which bisects the angle N2-N1-N3. X0 is meaningless in this context, and should be set to zero.

Examples of extra data:

To generate data for the plane through atoms 10, 11, and 20, use as extra
data: "1 10 11 20 0" (do not include the quotation marks.)
Alternatively, every datum can be expressed in keyword style, as "icase=1 n1=10
n2=11 n3=20 z0=0"