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edoapra authored Nov 1, 2023
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72 changes: 46 additions & 26 deletions Keywords-for-the-GEOMETRY-directive.md
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All of the keywords and input on this line are optional. The following
list describes all options and their defaults.

- `<name>` - user-supplied name for the geometry; the default name is
### NAME
`<name>` is a user-supplied name for the geometry; the default name is
geometry, and all NWChem modules look for a geometry with this name.
However, multiple geometries may be specified by using a different
name for each. Subsequently, the user can direct a module to a named
geometry by using the [SET](SET.md) directive (see the example in the [SET Section](SET.md))
to associate the default name of geometry with the alternate name.
- `units` - keyword specifying that a value will be entered by the user

### UNITS
The `units` keyword specifies what value will be entered by the user
for the string variable <units>. The default units for the geometry
input are Angstrøms (Note: atomic units or Bohr are used within the
code, regardless of the option specified for the input units. The
default conversion factor used in the code to convert from Angstrøms
to Bohr is 1.8897265 which may be overidden with the
`angstrom_to_au` keyword described below.).
The code recognizes the
following possible values for the string variable <units>:
- `angstroms` or `an` -- Angstroms , the default (converts to A.U.
using the Angstrom to A.U. conversion factor)
- `au` or `atomic` or `bohr` -- Atomic units (A.U.)
- `nm` or `nanometers` -- nanometers (converts to A.U. using a
conversion factor computed as 10.0 times the Angstrom to A.U.
conversion factor)
- `pm` or `picometers` -- `picometers` (converts to A.U. using a
conversion factor computed as 0.01 times the Angstrom to A.U.
conversion factor)
- `angstrom_to_au` - may also be specified as `ang2au`. This enables the
following possible values for the string variable <units>:
* `angstroms` or `an`: Angstrøms , the default (converts to A.U.
using the Angstrøm to A.U. conversion factor)
* `au` or `atomic` or `bohr`: Atomic units (A.U.)
* `nm` or `nanometers`: nanometers (converts to A.U. using a
conversion factor computed as 10.0 times the Angstrøm to A.U.
conversion factor)
* `pm` or `picometers`: `picometers` (converts to A.U. using a
conversion factor computed as 0.01 times the Angstrøm to A.U.
conversion factor)

### ANGSTROM_TO_AU
The `angstrom_to_au` option may also be specified as `ang2au`. This enables the
user to modify the conversion factors used to convert between
Angstrom and A.U.. The default value is 1.8897265.
- `bqbq` - keyword to specify the treatment of interactions between
Angstrøm and A.U.. The default value is 1.8897265.

### BQBQ
The `bqbq` keyword specifies the treatment of interactions between
dummy centers. The default in NWChem is to ignore such interactions
when computing energies or energy derivatives. These interactions
will be included if the keyword `bqbq` is specified.
- `print` and `noprint` - complementary keyword pair to enable or disable

### PRINT/NOPRINT
`print` and `noprint` is a complementary keyword pair to enable or disable
printing of the geometry. The default is to print the output
associated with the geometry. In addition, the keyword print may be
qualified by the additional keyword xyz, which specifies that the
coordinates should be printed in the XYZ format of molecular
graphics program XMol
- `center` and `nocenter` - complementary keyword pair to enable or

### CENTER/NOCENTER
`center` and `nocenter` is a complementary keyword pair to enable or
disable translation of the center of nuclear charge to the origin.
With the origin at this position, all three components of the
nuclear dipole are zero. The default is to move the center of
nuclear charge to the origin.
- `autosym` and `noautosym` - keyword to specify that the symmetry of the

### AUTOSYM/NOAUTOSYM
`autosym` and `noautosym` are keywords to specify that the symmetry of the
geometric system should be automatically determined. This option is
on by default, but can be turned off with noautosym. Only groups up
to and including O<sub>h</sub> are recognized. Occasionally NWChem will
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tags might be assigned different basis sets, for example, after
which they are no longer symmetry equivalent. Therefore autosym
chooses to make the save choice.
- `noautoz` - by default NWChem (release 3.3 and later) will generate

### NOAUTOZ

`noautoz` - by default NWChem (release 3.3 and later) will generate
redundant internal coordinates from user input Cartesian
coordinates. The internal coordinates will be used in geometry
optimizations. The `noautoz` keyword disables use of internal
Expand All @@ -87,19 +103,23 @@ list describes all options and their defaults.
a more detailed description of redundant internal coordinates,
including how to force the definition of specific internal variables
in combination with automatically generated variables.
- `adjust` - This indicates that an existing geometry is to be adjusted.

### ADJUST
Use of the `adjust` keyword indicates that an existing geometry is to be adjusted.
Only new input for the redundant internal coordinates may be
provided ([ZCOORD: Forcing internal
coordinates](ZCOORD-Forcing-internal-coordinates.md)). It
is not possible to define new centers or to modify the point group
using this keyword. See the section [use of the adjust keyword](ZCOORD-Forcing-internal-coordinates.md#how-to-use-the-adjust-keyword) for
an example of its usage.
- `nucleus` - keyword to specify the default model for the nuclear
charge distribution. The following values are recognized:
- `point` or `pt` -- point nuclear charge distribution. This is the
default.
- `finite` or `fi` -- finite nuclear charge distribution with a
Gaussian shape. The RMS radius of the Gaussian is determined

### NUCLEUS
The `nucleus` keyword to specifies the default model for the nuclear
charge distribution. The following values are recognized:
* `point` or `pt`: point nuclear charge distribution. This is the default.
* `finite` or `fi`: finite nuclear charge distribution with a
Gaussian shape.
The RMS radius of the Gaussian is determined
from the nuclear mass number A by the expression
<pre>r<sub> RMS</sub> = 0.836*A<sup>1/3</sup>+0.57 fm</pre>

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