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The EXTERNALS block key controls the input data for the MM atoms. If this block is not found no DRF calculation will be performed. For each MM atom the following data are required:
EXTERNALS
atm num grp-nam grp-num, char, x, y, x, pol
...
GROUP
{...}
end
atm
Type of atom, i.e., H, O, ...
num
number of atoms (optional)
grp-nam
Name of the group to which the atom belongs
grp-num
Number of the group to which the atom belong
char
atomic charge (in atomic units)
x
x-coordinate
y
y-coordinate
z
z-coordinate
pol
atomic polarizability (in atomic units)
GROUP
Indicates the end of group
The separation of molecules into GROUP's are important. Since in the many-body polarization operator only inter-molecular interactions, i.e. only interaction between sites which do not belong to the some group, are included. Therefore, it is important that the combined string (grp-nam + grp-num) is unique for each GROUP.
An example of a EXTERNALS block for two water molecules:
EXTERNALS
O 4 water 2, -0.6690, -11.380487, -11.810553, -4.515226, 9.3005
H 5 water 2, 0.3345, -13.104751, -11.837669, -3.969549, 0.0690
H 6 water 2, 0.3345, -10.510898, -12.853311, -3.320199, 0.0690
GROUP
O 7 water 3, -0.6690, -1.116350, 9.119186, -3.230948, 9.3005
H 8 water 3, 0.3345, -2.822714, 9.717033, -3.180632, 0.0690
H 9 water 3, 0.3345, -0.123788, 10.538199, -2.708607, 0.0690
GROUP
{...}
end